From 808f8a7a77d56f65dd4a4643dd66158f106ab755 Mon Sep 17 00:00:00 2001
From: Stephen Haberman <stephen.haberman@gmail.com>
Date: Sun, 28 Nov 2021 08:31:29 -0600
Subject: [PATCH] feat: Use exact types for fromPartial (#412)

* Add proof-of-concept exact types.

Fixes #156.

* Extract Builtin.

* Codegen.

* Add expect error.

* Codegen again.

* Fix type registry.
---
 integration/angular/simple-message.ts         |  8 +-
 integration/avoid-import-conflicts/simple.ts  | 10 ++-
 integration/avoid-import-conflicts/simple2.ts |  8 +-
 integration/barrel-imports/bar.ts             |  8 +-
 integration/barrel-imports/foo.ts             |  8 +-
 integration/batching-with-context/batching.ts | 34 ++++---
 integration/batching/batching.ts              | 34 ++++---
 integration/bytes-as-base64/message.ts        |  8 +-
 integration/bytes-node/point.ts               |  8 +-
 integration/const-enum/const-enum.ts          |  8 +-
 .../generic-service-definitions/simple.ts     |  8 +-
 integration/global-this/global-this.ts        | 10 ++-
 integration/grpc-js/google/protobuf/empty.ts  |  8 +-
 integration/grpc-js/google/protobuf/struct.ts | 16 ++--
 .../grpc-js/google/protobuf/timestamp.ts      |  8 +-
 .../grpc-js/google/protobuf/wrappers.ts       | 24 +++--
 integration/grpc-js/simple.ts                 |  8 +-
 integration/grpc-web-go-server/example.ts     | 24 +++--
 .../example.ts                                | 16 ++--
 integration/grpc-web-no-streaming/example.ts  | 16 ++--
 integration/grpc-web/example.ts               | 24 +++--
 integration/lower-case-svc-methods/math.ts    | 14 ++-
 .../no-proto-package/no-proto-package.ts      | 10 ++-
 integration/oneof-properties/oneof.ts         | 10 ++-
 integration/oneof-unions/oneof.ts             | 12 ++-
 integration/point/point.ts                    | 10 ++-
 integration/return-observable/observable.ts   | 10 ++-
 .../simple-deprecated-fields/simple.ts        | 10 ++-
 integration/simple-esmodule-interop/simple.ts | 10 ++-
 .../google/protobuf/timestamp.ts              |  8 +-
 integration/simple-json-name/simple.ts        |  8 +-
 .../google/protobuf/timestamp.ts              |  8 +-
 .../google/protobuf/wrappers.ts               | 24 +++--
 integration/simple-long-string/simple.ts      |  8 +-
 .../simple-long/google/protobuf/wrappers.ts   | 24 +++--
 integration/simple-long/simple.ts             | 28 ++++--
 .../google/protobuf/timestamp.ts              |  8 +-
 .../google/protobuf/wrappers.ts               | 24 +++--
 .../simple-optionals/import_dir/thing.ts      |  8 +-
 integration/simple-optionals/simple.ts        | 60 ++++++++-----
 integration/simple-optionals/thing.ts         |  8 +-
 integration/simple-proto2/simple.ts           |  8 +-
 .../simple-snake/google/protobuf/timestamp.ts |  8 +-
 .../simple-snake/google/protobuf/wrappers.ts  | 24 +++--
 integration/simple-snake/import_dir/thing.ts  |  8 +-
 integration/simple-snake/simple.ts            | 60 ++++++++-----
 integration/simple-string-enums/simple.ts     | 10 ++-
 .../google/protobuf/timestamp.ts              |  8 +-
 .../google/protobuf/wrappers.ts               | 24 +++--
 .../import_dir/thing.ts                       |  8 +-
 .../simple-unrecognized-enum/simple.ts        | 60 ++++++++-----
 .../simple/google/protobuf/timestamp.ts       |  8 +-
 .../simple/google/protobuf/wrappers.ts        | 24 +++--
 integration/simple/google/type/date.ts        |  8 +-
 integration/simple/import_dir/thing.ts        |  8 +-
 integration/simple/simple-test.ts             |  7 ++
 integration/simple/simple.ts                  | 88 ++++++++++++-------
 integration/struct/google/protobuf/struct.ts  | 16 ++--
 integration/struct/struct.ts                  |  8 +-
 integration/type-registry/bar/bar.ts          |  8 +-
 integration/type-registry/foo.ts              | 10 ++-
 .../google/protobuf/timestamp.ts              |  8 +-
 integration/types-with-underscores/file.ts    | 10 ++-
 .../google/protobuf/timestamp.ts              |  8 +-
 integration/use-date-false/metadata.ts        |  8 +-
 .../google/protobuf/timestamp.ts              |  8 +-
 .../use-date-string/use-date-string.ts        | 12 ++-
 .../google/protobuf/timestamp.ts              |  8 +-
 integration/use-date-true/use-date-true.ts    | 12 ++-
 integration/value/google/protobuf/struct.ts   | 16 ++--
 integration/value/google/protobuf/wrappers.ts | 24 +++--
 integration/value/value.ts                    | 10 ++-
 integration/vector-tile/vector_tile.ts        | 26 +++---
 src/generate-type-registry.ts                 |  2 +-
 src/main.ts                                   | 30 +++++--
 75 files changed, 845 insertions(+), 338 deletions(-)

diff --git a/integration/angular/simple-message.ts b/integration/angular/simple-message.ts
index 1db847db3..356091ac8 100644
--- a/integration/angular/simple-message.ts
+++ b/integration/angular/simple-message.ts
@@ -49,7 +49,7 @@ export const SimpleMessage = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<SimpleMessage>): SimpleMessage {
+  fromPartial<I extends Exact<DeepPartial<SimpleMessage>, I>>(object: I): SimpleMessage {
     const message = { ...baseSimpleMessage } as SimpleMessage;
     message.numberField = object.numberField ?? 0;
     return message;
@@ -57,6 +57,7 @@ export const SimpleMessage = {
 };
 
 type Builtin = Date | Function | Uint8Array | string | number | boolean | undefined;
+
 export type DeepPartial<T> = T extends Builtin
   ? T
   : T extends Array<infer U>
@@ -67,6 +68,11 @@ export type DeepPartial<T> = T extends Builtin
   ? { [K in keyof T]?: DeepPartial<T[K]> }
   : Partial<T>;
 
+type KeysOfUnion<T> = T extends T ? keyof T : never;
+export type Exact<P, I extends P> = P extends Builtin
+  ? P
+  : P & { [K in keyof P]: Exact<P[K], I[K]> } & Record<Exclude<keyof I, KeysOfUnion<P>>, never>;
+
 // If you get a compile-error about 'Constructor<Long> and ... have no overlap',
 // add '--ts_proto_opt=esModuleInterop=true' as a flag when calling 'protoc'.
 if (util.Long !== Long) {
diff --git a/integration/avoid-import-conflicts/simple.ts b/integration/avoid-import-conflicts/simple.ts
index 4afd4c318..9b43915bc 100644
--- a/integration/avoid-import-conflicts/simple.ts
+++ b/integration/avoid-import-conflicts/simple.ts
@@ -110,7 +110,7 @@ export const Simple = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Simple>): Simple {
+  fromPartial<I extends Exact<DeepPartial<Simple>, I>>(object: I): Simple {
     const message = { ...baseSimple } as Simple;
     message.name = object.name ?? '';
     message.otherSimple =
@@ -171,7 +171,7 @@ export const SimpleEnums = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<SimpleEnums>): SimpleEnums {
+  fromPartial<I extends Exact<DeepPartial<SimpleEnums>, I>>(object: I): SimpleEnums {
     const message = { ...baseSimpleEnums } as SimpleEnums;
     message.localEnum = object.localEnum ?? 0;
     message.importEnum = object.importEnum ?? 0;
@@ -180,6 +180,7 @@ export const SimpleEnums = {
 };
 
 type Builtin = Date | Function | Uint8Array | string | number | boolean | undefined;
+
 export type DeepPartial<T> = T extends Builtin
   ? T
   : T extends Array<infer U>
@@ -190,6 +191,11 @@ export type DeepPartial<T> = T extends Builtin
   ? { [K in keyof T]?: DeepPartial<T[K]> }
   : Partial<T>;
 
+type KeysOfUnion<T> = T extends T ? keyof T : never;
+export type Exact<P, I extends P> = P extends Builtin
+  ? P
+  : P & { [K in keyof P]: Exact<P[K], I[K]> } & Record<Exclude<keyof I, KeysOfUnion<P>>, never>;
+
 // If you get a compile-error about 'Constructor<Long> and ... have no overlap',
 // add '--ts_proto_opt=esModuleInterop=true' as a flag when calling 'protoc'.
 if (util.Long !== Long) {
diff --git a/integration/avoid-import-conflicts/simple2.ts b/integration/avoid-import-conflicts/simple2.ts
index 417895041..214706ce7 100644
--- a/integration/avoid-import-conflicts/simple2.ts
+++ b/integration/avoid-import-conflicts/simple2.ts
@@ -95,7 +95,7 @@ export const Simple = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Simple>): Simple {
+  fromPartial<I extends Exact<DeepPartial<Simple>, I>>(object: I): Simple {
     const message = { ...baseSimple } as Simple;
     message.name = object.name ?? '';
     message.age = object.age ?? 0;
@@ -104,6 +104,7 @@ export const Simple = {
 };
 
 type Builtin = Date | Function | Uint8Array | string | number | boolean | undefined;
+
 export type DeepPartial<T> = T extends Builtin
   ? T
   : T extends Array<infer U>
@@ -114,6 +115,11 @@ export type DeepPartial<T> = T extends Builtin
   ? { [K in keyof T]?: DeepPartial<T[K]> }
   : Partial<T>;
 
+type KeysOfUnion<T> = T extends T ? keyof T : never;
+export type Exact<P, I extends P> = P extends Builtin
+  ? P
+  : P & { [K in keyof P]: Exact<P[K], I[K]> } & Record<Exclude<keyof I, KeysOfUnion<P>>, never>;
+
 // If you get a compile-error about 'Constructor<Long> and ... have no overlap',
 // add '--ts_proto_opt=esModuleInterop=true' as a flag when calling 'protoc'.
 if (util.Long !== Long) {
diff --git a/integration/barrel-imports/bar.ts b/integration/barrel-imports/bar.ts
index 96cb2248f..261cbd7c8 100644
--- a/integration/barrel-imports/bar.ts
+++ b/integration/barrel-imports/bar.ts
@@ -55,7 +55,7 @@ export const Bar = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Bar>): Bar {
+  fromPartial<I extends Exact<DeepPartial<Bar>, I>>(object: I): Bar {
     const message = { ...baseBar } as Bar;
     message.name = object.name ?? '';
     message.age = object.age ?? 0;
@@ -64,6 +64,7 @@ export const Bar = {
 };
 
 type Builtin = Date | Function | Uint8Array | string | number | boolean | undefined;
+
 type DeepPartial<T> = T extends Builtin
   ? T
   : T extends Array<infer U>
@@ -74,6 +75,11 @@ type DeepPartial<T> = T extends Builtin
   ? { [K in keyof T]?: DeepPartial<T[K]> }
   : Partial<T>;
 
+type KeysOfUnion<T> = T extends T ? keyof T : never;
+type Exact<P, I extends P> = P extends Builtin
+  ? P
+  : P & { [K in keyof P]: Exact<P[K], I[K]> } & Record<Exclude<keyof I, KeysOfUnion<P>>, never>;
+
 // If you get a compile-error about 'Constructor<Long> and ... have no overlap',
 // add '--ts_proto_opt=esModuleInterop=true' as a flag when calling 'protoc'.
 if (util.Long !== Long) {
diff --git a/integration/barrel-imports/foo.ts b/integration/barrel-imports/foo.ts
index 9a48e8127..548d2cff1 100644
--- a/integration/barrel-imports/foo.ts
+++ b/integration/barrel-imports/foo.ts
@@ -56,7 +56,7 @@ export const Foo = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Foo>): Foo {
+  fromPartial<I extends Exact<DeepPartial<Foo>, I>>(object: I): Foo {
     const message = { ...baseFoo } as Foo;
     message.name = object.name ?? '';
     message.bar = object.bar !== undefined && object.bar !== null ? Bar.fromPartial(object.bar) : undefined;
@@ -65,6 +65,7 @@ export const Foo = {
 };
 
 type Builtin = Date | Function | Uint8Array | string | number | boolean | undefined;
+
 type DeepPartial<T> = T extends Builtin
   ? T
   : T extends Array<infer U>
@@ -75,6 +76,11 @@ type DeepPartial<T> = T extends Builtin
   ? { [K in keyof T]?: DeepPartial<T[K]> }
   : Partial<T>;
 
+type KeysOfUnion<T> = T extends T ? keyof T : never;
+type Exact<P, I extends P> = P extends Builtin
+  ? P
+  : P & { [K in keyof P]: Exact<P[K], I[K]> } & Record<Exclude<keyof I, KeysOfUnion<P>>, never>;
+
 // If you get a compile-error about 'Constructor<Long> and ... have no overlap',
 // add '--ts_proto_opt=esModuleInterop=true' as a flag when calling 'protoc'.
 if (util.Long !== Long) {
diff --git a/integration/batching-with-context/batching.ts b/integration/batching-with-context/batching.ts
index 4da12298a..719bf95ea 100644
--- a/integration/batching-with-context/batching.ts
+++ b/integration/batching-with-context/batching.ts
@@ -91,9 +91,9 @@ export const BatchQueryRequest = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<BatchQueryRequest>): BatchQueryRequest {
+  fromPartial<I extends Exact<DeepPartial<BatchQueryRequest>, I>>(object: I): BatchQueryRequest {
     const message = { ...baseBatchQueryRequest } as BatchQueryRequest;
-    message.ids = (object.ids ?? []).map((e) => e);
+    message.ids = object.ids?.map((e) => e) || [];
     return message;
   },
 };
@@ -143,9 +143,9 @@ export const BatchQueryResponse = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<BatchQueryResponse>): BatchQueryResponse {
+  fromPartial<I extends Exact<DeepPartial<BatchQueryResponse>, I>>(object: I): BatchQueryResponse {
     const message = { ...baseBatchQueryResponse } as BatchQueryResponse;
-    message.entities = (object.entities ?? []).map((e) => Entity.fromPartial(e));
+    message.entities = object.entities?.map((e) => Entity.fromPartial(e)) || [];
     return message;
   },
 };
@@ -195,9 +195,9 @@ export const BatchMapQueryRequest = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<BatchMapQueryRequest>): BatchMapQueryRequest {
+  fromPartial<I extends Exact<DeepPartial<BatchMapQueryRequest>, I>>(object: I): BatchMapQueryRequest {
     const message = { ...baseBatchMapQueryRequest } as BatchMapQueryRequest;
-    message.ids = (object.ids ?? []).map((e) => e);
+    message.ids = object.ids?.map((e) => e) || [];
     return message;
   },
 };
@@ -254,7 +254,7 @@ export const BatchMapQueryResponse = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<BatchMapQueryResponse>): BatchMapQueryResponse {
+  fromPartial<I extends Exact<DeepPartial<BatchMapQueryResponse>, I>>(object: I): BatchMapQueryResponse {
     const message = { ...baseBatchMapQueryResponse } as BatchMapQueryResponse;
     message.entities = Object.entries(object.entities ?? {}).reduce<{ [key: string]: Entity }>((acc, [key, value]) => {
       if (value !== undefined) {
@@ -314,7 +314,9 @@ export const BatchMapQueryResponse_EntitiesEntry = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<BatchMapQueryResponse_EntitiesEntry>): BatchMapQueryResponse_EntitiesEntry {
+  fromPartial<I extends Exact<DeepPartial<BatchMapQueryResponse_EntitiesEntry>, I>>(
+    object: I
+  ): BatchMapQueryResponse_EntitiesEntry {
     const message = { ...baseBatchMapQueryResponse_EntitiesEntry } as BatchMapQueryResponse_EntitiesEntry;
     message.key = object.key ?? '';
     message.value = object.value !== undefined && object.value !== null ? Entity.fromPartial(object.value) : undefined;
@@ -362,7 +364,7 @@ export const GetOnlyMethodRequest = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<GetOnlyMethodRequest>): GetOnlyMethodRequest {
+  fromPartial<I extends Exact<DeepPartial<GetOnlyMethodRequest>, I>>(object: I): GetOnlyMethodRequest {
     const message = { ...baseGetOnlyMethodRequest } as GetOnlyMethodRequest;
     message.id = object.id ?? '';
     return message;
@@ -409,7 +411,7 @@ export const GetOnlyMethodResponse = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<GetOnlyMethodResponse>): GetOnlyMethodResponse {
+  fromPartial<I extends Exact<DeepPartial<GetOnlyMethodResponse>, I>>(object: I): GetOnlyMethodResponse {
     const message = { ...baseGetOnlyMethodResponse } as GetOnlyMethodResponse;
     message.entity =
       object.entity !== undefined && object.entity !== null ? Entity.fromPartial(object.entity) : undefined;
@@ -457,7 +459,7 @@ export const WriteMethodRequest = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<WriteMethodRequest>): WriteMethodRequest {
+  fromPartial<I extends Exact<DeepPartial<WriteMethodRequest>, I>>(object: I): WriteMethodRequest {
     const message = { ...baseWriteMethodRequest } as WriteMethodRequest;
     message.id = object.id ?? '';
     return message;
@@ -496,7 +498,7 @@ export const WriteMethodResponse = {
     return obj;
   },
 
-  fromPartial(_: DeepPartial<WriteMethodResponse>): WriteMethodResponse {
+  fromPartial<I extends Exact<DeepPartial<WriteMethodResponse>, I>>(_: I): WriteMethodResponse {
     const message = { ...baseWriteMethodResponse } as WriteMethodResponse;
     return message;
   },
@@ -550,7 +552,7 @@ export const Entity = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Entity>): Entity {
+  fromPartial<I extends Exact<DeepPartial<Entity>, I>>(object: I): Entity {
     const message = { ...baseEntity } as Entity;
     message.id = object.id ?? '';
     message.name = object.name ?? '';
@@ -656,6 +658,7 @@ export interface DataLoaders {
 }
 
 type Builtin = Date | Function | Uint8Array | string | number | boolean | undefined;
+
 export type DeepPartial<T> = T extends Builtin
   ? T
   : T extends Array<infer U>
@@ -666,6 +669,11 @@ export type DeepPartial<T> = T extends Builtin
   ? { [K in keyof T]?: DeepPartial<T[K]> }
   : Partial<T>;
 
+type KeysOfUnion<T> = T extends T ? keyof T : never;
+export type Exact<P, I extends P> = P extends Builtin
+  ? P
+  : P & { [K in keyof P]: Exact<P[K], I[K]> } & Record<Exclude<keyof I, KeysOfUnion<P>>, never>;
+
 // If you get a compile-error about 'Constructor<Long> and ... have no overlap',
 // add '--ts_proto_opt=esModuleInterop=true' as a flag when calling 'protoc'.
 if (util.Long !== Long) {
diff --git a/integration/batching/batching.ts b/integration/batching/batching.ts
index 1aa547719..9a73f86e1 100644
--- a/integration/batching/batching.ts
+++ b/integration/batching/batching.ts
@@ -89,9 +89,9 @@ export const BatchQueryRequest = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<BatchQueryRequest>): BatchQueryRequest {
+  fromPartial<I extends Exact<DeepPartial<BatchQueryRequest>, I>>(object: I): BatchQueryRequest {
     const message = { ...baseBatchQueryRequest } as BatchQueryRequest;
-    message.ids = (object.ids ?? []).map((e) => e);
+    message.ids = object.ids?.map((e) => e) || [];
     return message;
   },
 };
@@ -141,9 +141,9 @@ export const BatchQueryResponse = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<BatchQueryResponse>): BatchQueryResponse {
+  fromPartial<I extends Exact<DeepPartial<BatchQueryResponse>, I>>(object: I): BatchQueryResponse {
     const message = { ...baseBatchQueryResponse } as BatchQueryResponse;
-    message.entities = (object.entities ?? []).map((e) => Entity.fromPartial(e));
+    message.entities = object.entities?.map((e) => Entity.fromPartial(e)) || [];
     return message;
   },
 };
@@ -193,9 +193,9 @@ export const BatchMapQueryRequest = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<BatchMapQueryRequest>): BatchMapQueryRequest {
+  fromPartial<I extends Exact<DeepPartial<BatchMapQueryRequest>, I>>(object: I): BatchMapQueryRequest {
     const message = { ...baseBatchMapQueryRequest } as BatchMapQueryRequest;
-    message.ids = (object.ids ?? []).map((e) => e);
+    message.ids = object.ids?.map((e) => e) || [];
     return message;
   },
 };
@@ -252,7 +252,7 @@ export const BatchMapQueryResponse = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<BatchMapQueryResponse>): BatchMapQueryResponse {
+  fromPartial<I extends Exact<DeepPartial<BatchMapQueryResponse>, I>>(object: I): BatchMapQueryResponse {
     const message = { ...baseBatchMapQueryResponse } as BatchMapQueryResponse;
     message.entities = Object.entries(object.entities ?? {}).reduce<{ [key: string]: Entity }>((acc, [key, value]) => {
       if (value !== undefined) {
@@ -312,7 +312,9 @@ export const BatchMapQueryResponse_EntitiesEntry = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<BatchMapQueryResponse_EntitiesEntry>): BatchMapQueryResponse_EntitiesEntry {
+  fromPartial<I extends Exact<DeepPartial<BatchMapQueryResponse_EntitiesEntry>, I>>(
+    object: I
+  ): BatchMapQueryResponse_EntitiesEntry {
     const message = { ...baseBatchMapQueryResponse_EntitiesEntry } as BatchMapQueryResponse_EntitiesEntry;
     message.key = object.key ?? '';
     message.value = object.value !== undefined && object.value !== null ? Entity.fromPartial(object.value) : undefined;
@@ -360,7 +362,7 @@ export const GetOnlyMethodRequest = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<GetOnlyMethodRequest>): GetOnlyMethodRequest {
+  fromPartial<I extends Exact<DeepPartial<GetOnlyMethodRequest>, I>>(object: I): GetOnlyMethodRequest {
     const message = { ...baseGetOnlyMethodRequest } as GetOnlyMethodRequest;
     message.id = object.id ?? '';
     return message;
@@ -407,7 +409,7 @@ export const GetOnlyMethodResponse = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<GetOnlyMethodResponse>): GetOnlyMethodResponse {
+  fromPartial<I extends Exact<DeepPartial<GetOnlyMethodResponse>, I>>(object: I): GetOnlyMethodResponse {
     const message = { ...baseGetOnlyMethodResponse } as GetOnlyMethodResponse;
     message.entity =
       object.entity !== undefined && object.entity !== null ? Entity.fromPartial(object.entity) : undefined;
@@ -455,7 +457,7 @@ export const WriteMethodRequest = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<WriteMethodRequest>): WriteMethodRequest {
+  fromPartial<I extends Exact<DeepPartial<WriteMethodRequest>, I>>(object: I): WriteMethodRequest {
     const message = { ...baseWriteMethodRequest } as WriteMethodRequest;
     message.id = object.id ?? '';
     return message;
@@ -494,7 +496,7 @@ export const WriteMethodResponse = {
     return obj;
   },
 
-  fromPartial(_: DeepPartial<WriteMethodResponse>): WriteMethodResponse {
+  fromPartial<I extends Exact<DeepPartial<WriteMethodResponse>, I>>(_: I): WriteMethodResponse {
     const message = { ...baseWriteMethodResponse } as WriteMethodResponse;
     return message;
   },
@@ -548,7 +550,7 @@ export const Entity = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Entity>): Entity {
+  fromPartial<I extends Exact<DeepPartial<Entity>, I>>(object: I): Entity {
     const message = { ...baseEntity } as Entity;
     message.id = object.id ?? '';
     message.name = object.name ?? '';
@@ -604,6 +606,7 @@ interface Rpc {
 }
 
 type Builtin = Date | Function | Uint8Array | string | number | boolean | undefined;
+
 export type DeepPartial<T> = T extends Builtin
   ? T
   : T extends Array<infer U>
@@ -614,6 +617,11 @@ export type DeepPartial<T> = T extends Builtin
   ? { [K in keyof T]?: DeepPartial<T[K]> }
   : Partial<T>;
 
+type KeysOfUnion<T> = T extends T ? keyof T : never;
+export type Exact<P, I extends P> = P extends Builtin
+  ? P
+  : P & { [K in keyof P]: Exact<P[K], I[K]> } & Record<Exclude<keyof I, KeysOfUnion<P>>, never>;
+
 // If you get a compile-error about 'Constructor<Long> and ... have no overlap',
 // add '--ts_proto_opt=esModuleInterop=true' as a flag when calling 'protoc'.
 if (util.Long !== Long) {
diff --git a/integration/bytes-as-base64/message.ts b/integration/bytes-as-base64/message.ts
index 72bc4928a..bfbd42460 100644
--- a/integration/bytes-as-base64/message.ts
+++ b/integration/bytes-as-base64/message.ts
@@ -24,7 +24,7 @@ export const Message = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Message>): Message {
+  fromPartial<I extends Exact<DeepPartial<Message>, I>>(object: I): Message {
     const message = { ...baseMessage } as Message;
     message.data = object.data ?? new Uint8Array();
     return message;
@@ -64,6 +64,7 @@ function base64FromBytes(arr: Uint8Array): string {
 }
 
 type Builtin = Date | Function | Uint8Array | string | number | boolean | undefined;
+
 export type DeepPartial<T> = T extends Builtin
   ? T
   : T extends Array<infer U>
@@ -74,6 +75,11 @@ export type DeepPartial<T> = T extends Builtin
   ? { [K in keyof T]?: DeepPartial<T[K]> }
   : Partial<T>;
 
+type KeysOfUnion<T> = T extends T ? keyof T : never;
+export type Exact<P, I extends P> = P extends Builtin
+  ? P
+  : P & { [K in keyof P]: Exact<P[K], I[K]> } & Record<Exclude<keyof I, KeysOfUnion<P>>, never>;
+
 // If you get a compile-error about 'Constructor<Long> and ... have no overlap',
 // add '--ts_proto_opt=esModuleInterop=true' as a flag when calling 'protoc'.
 if (util.Long !== Long) {
diff --git a/integration/bytes-node/point.ts b/integration/bytes-node/point.ts
index de913dcba..14f43a529 100644
--- a/integration/bytes-node/point.ts
+++ b/integration/bytes-node/point.ts
@@ -51,7 +51,7 @@ export const Point = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Point>): Point {
+  fromPartial<I extends Exact<DeepPartial<Point>, I>>(object: I): Point {
     const message = { ...basePoint } as Point;
     message.data = object.data ?? Buffer.alloc(0);
     return message;
@@ -91,6 +91,7 @@ function base64FromBytes(arr: Uint8Array): string {
 }
 
 type Builtin = Date | Function | Uint8Array | string | number | boolean | undefined;
+
 export type DeepPartial<T> = T extends Builtin
   ? T
   : T extends Array<infer U>
@@ -101,6 +102,11 @@ export type DeepPartial<T> = T extends Builtin
   ? { [K in keyof T]?: DeepPartial<T[K]> }
   : Partial<T>;
 
+type KeysOfUnion<T> = T extends T ? keyof T : never;
+export type Exact<P, I extends P> = P extends Builtin
+  ? P
+  : P & { [K in keyof P]: Exact<P[K], I[K]> } & Record<Exclude<keyof I, KeysOfUnion<P>>, never>;
+
 // If you get a compile-error about 'Constructor<Long> and ... have no overlap',
 // add '--ts_proto_opt=esModuleInterop=true' as a flag when calling 'protoc'.
 if (util.Long !== Long) {
diff --git a/integration/const-enum/const-enum.ts b/integration/const-enum/const-enum.ts
index 6af20d49e..428b27e15 100644
--- a/integration/const-enum/const-enum.ts
+++ b/integration/const-enum/const-enum.ts
@@ -110,7 +110,7 @@ export const DividerData = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<DividerData>): DividerData {
+  fromPartial<I extends Exact<DeepPartial<DividerData>, I>>(object: I): DividerData {
     const message = { ...baseDividerData } as DividerData;
     message.type = object.type ?? DividerData_DividerType.DOUBLE;
     return message;
@@ -118,6 +118,7 @@ export const DividerData = {
 };
 
 type Builtin = Date | Function | Uint8Array | string | number | boolean | undefined;
+
 export type DeepPartial<T> = T extends Builtin
   ? T
   : T extends Array<infer U>
@@ -128,6 +129,11 @@ export type DeepPartial<T> = T extends Builtin
   ? { [K in keyof T]?: DeepPartial<T[K]> }
   : Partial<T>;
 
+type KeysOfUnion<T> = T extends T ? keyof T : never;
+export type Exact<P, I extends P> = P extends Builtin
+  ? P
+  : P & { [K in keyof P]: Exact<P[K], I[K]> } & Record<Exclude<keyof I, KeysOfUnion<P>>, never>;
+
 // If you get a compile-error about 'Constructor<Long> and ... have no overlap',
 // add '--ts_proto_opt=esModuleInterop=true' as a flag when calling 'protoc'.
 if (util.Long !== Long) {
diff --git a/integration/generic-service-definitions/simple.ts b/integration/generic-service-definitions/simple.ts
index 32d61ee0f..4d1894dd5 100644
--- a/integration/generic-service-definitions/simple.ts
+++ b/integration/generic-service-definitions/simple.ts
@@ -48,7 +48,7 @@ export const TestMessage = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<TestMessage>): TestMessage {
+  fromPartial<I extends Exact<DeepPartial<TestMessage>, I>>(object: I): TestMessage {
     const message = { ...baseTestMessage } as TestMessage;
     message.value = object.value ?? '';
     return message;
@@ -125,6 +125,7 @@ export const TestDefinition = {
 } as const;
 
 type Builtin = Date | Function | Uint8Array | string | number | boolean | undefined;
+
 export type DeepPartial<T> = T extends Builtin
   ? T
   : T extends Array<infer U>
@@ -135,6 +136,11 @@ export type DeepPartial<T> = T extends Builtin
   ? { [K in keyof T]?: DeepPartial<T[K]> }
   : Partial<T>;
 
+type KeysOfUnion<T> = T extends T ? keyof T : never;
+export type Exact<P, I extends P> = P extends Builtin
+  ? P
+  : P & { [K in keyof P]: Exact<P[K], I[K]> } & Record<Exclude<keyof I, KeysOfUnion<P>>, never>;
+
 // If you get a compile-error about 'Constructor<Long> and ... have no overlap',
 // add '--ts_proto_opt=esModuleInterop=true' as a flag when calling 'protoc'.
 if (util.Long !== Long) {
diff --git a/integration/global-this/global-this.ts b/integration/global-this/global-this.ts
index 70f23822b..f80ff78c1 100644
--- a/integration/global-this/global-this.ts
+++ b/integration/global-this/global-this.ts
@@ -52,7 +52,7 @@ export const Object = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Object>): Object {
+  fromPartial<I extends Exact<DeepPartial<Object>, I>>(object: I): Object {
     const message = { ...baseObject } as Object;
     message.name = object.name ?? '';
     return message;
@@ -99,7 +99,7 @@ export const Error = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Error>): Error {
+  fromPartial<I extends Exact<DeepPartial<Error>, I>>(object: I): Error {
     const message = { ...baseError } as Error;
     message.name = object.name ?? '';
     return message;
@@ -107,6 +107,7 @@ export const Error = {
 };
 
 type Builtin = Date | Function | Uint8Array | string | number | boolean | undefined;
+
 export type DeepPartial<T> = T extends Builtin
   ? T
   : T extends Array<infer U>
@@ -117,6 +118,11 @@ export type DeepPartial<T> = T extends Builtin
   ? { [K in keyof T]?: DeepPartial<T[K]> }
   : Partial<T>;
 
+type KeysOfUnion<T> = T extends T ? keyof T : never;
+export type Exact<P, I extends P> = P extends Builtin
+  ? P
+  : P & { [K in keyof P]: Exact<P[K], I[K]> } & Record<Exclude<keyof I, KeysOfUnion<P>>, never>;
+
 // If you get a compile-error about 'Constructor<Long> and ... have no overlap',
 // add '--ts_proto_opt=esModuleInterop=true' as a flag when calling 'protoc'.
 if (util.Long !== Long) {
diff --git a/integration/grpc-js/google/protobuf/empty.ts b/integration/grpc-js/google/protobuf/empty.ts
index 185df6552..2370dce9e 100644
--- a/integration/grpc-js/google/protobuf/empty.ts
+++ b/integration/grpc-js/google/protobuf/empty.ts
@@ -49,13 +49,14 @@ export const Empty = {
     return obj;
   },
 
-  fromPartial(_: DeepPartial<Empty>): Empty {
+  fromPartial<I extends Exact<DeepPartial<Empty>, I>>(_: I): Empty {
     const message = { ...baseEmpty } as Empty;
     return message;
   },
 };
 
 type Builtin = Date | Function | Uint8Array | string | number | boolean | undefined;
+
 export type DeepPartial<T> = T extends Builtin
   ? T
   : T extends Array<infer U>
@@ -66,6 +67,11 @@ export type DeepPartial<T> = T extends Builtin
   ? { [K in keyof T]?: DeepPartial<T[K]> }
   : Partial<T>;
 
+type KeysOfUnion<T> = T extends T ? keyof T : never;
+export type Exact<P, I extends P> = P extends Builtin
+  ? P
+  : P & { [K in keyof P]: Exact<P[K], I[K]> } & Record<Exclude<keyof I, KeysOfUnion<P>>, never>;
+
 // If you get a compile-error about 'Constructor<Long> and ... have no overlap',
 // add '--ts_proto_opt=esModuleInterop=true' as a flag when calling 'protoc'.
 if (util.Long !== Long) {
diff --git a/integration/grpc-js/google/protobuf/struct.ts b/integration/grpc-js/google/protobuf/struct.ts
index a2b7d6f54..28fe05424 100644
--- a/integration/grpc-js/google/protobuf/struct.ts
+++ b/integration/grpc-js/google/protobuf/struct.ts
@@ -147,7 +147,7 @@ export const Struct = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Struct>): Struct {
+  fromPartial<I extends Exact<DeepPartial<Struct>, I>>(object: I): Struct {
     const message = { ...baseStruct } as Struct;
     message.fields = Object.entries(object.fields ?? {}).reduce<{ [key: string]: any | undefined }>(
       (acc, [key, value]) => {
@@ -228,7 +228,7 @@ export const Struct_FieldsEntry = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Struct_FieldsEntry>): Struct_FieldsEntry {
+  fromPartial<I extends Exact<DeepPartial<Struct_FieldsEntry>, I>>(object: I): Struct_FieldsEntry {
     const message = { ...baseStruct_FieldsEntry } as Struct_FieldsEntry;
     message.key = object.key ?? '';
     message.value = object.value ?? undefined;
@@ -321,7 +321,7 @@ export const Value = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Value>): Value {
+  fromPartial<I extends Exact<DeepPartial<Value>, I>>(object: I): Value {
     const message = { ...baseValue } as Value;
     message.nullValue = object.nullValue ?? undefined;
     message.numberValue = object.numberValue ?? undefined;
@@ -414,9 +414,9 @@ export const ListValue = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<ListValue>): ListValue {
+  fromPartial<I extends Exact<DeepPartial<ListValue>, I>>(object: I): ListValue {
     const message = { ...baseListValue } as ListValue;
-    message.values = (object.values ?? []).map((e) => e);
+    message.values = object.values?.map((e) => e) || [];
     return message;
   },
 
@@ -430,6 +430,7 @@ export const ListValue = {
 };
 
 type Builtin = Date | Function | Uint8Array | string | number | boolean | undefined;
+
 export type DeepPartial<T> = T extends Builtin
   ? T
   : T extends Array<infer U>
@@ -440,6 +441,11 @@ export type DeepPartial<T> = T extends Builtin
   ? { [K in keyof T]?: DeepPartial<T[K]> }
   : Partial<T>;
 
+type KeysOfUnion<T> = T extends T ? keyof T : never;
+export type Exact<P, I extends P> = P extends Builtin
+  ? P
+  : P & { [K in keyof P]: Exact<P[K], I[K]> } & Record<Exclude<keyof I, KeysOfUnion<P>>, never>;
+
 // If you get a compile-error about 'Constructor<Long> and ... have no overlap',
 // add '--ts_proto_opt=esModuleInterop=true' as a flag when calling 'protoc'.
 if (util.Long !== Long) {
diff --git a/integration/grpc-js/google/protobuf/timestamp.ts b/integration/grpc-js/google/protobuf/timestamp.ts
index e4600a73e..0670c17fd 100644
--- a/integration/grpc-js/google/protobuf/timestamp.ts
+++ b/integration/grpc-js/google/protobuf/timestamp.ts
@@ -161,7 +161,7 @@ export const Timestamp = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Timestamp>): Timestamp {
+  fromPartial<I extends Exact<DeepPartial<Timestamp>, I>>(object: I): Timestamp {
     const message = { ...baseTimestamp } as Timestamp;
     message.seconds = object.seconds ?? 0;
     message.nanos = object.nanos ?? 0;
@@ -181,6 +181,7 @@ var globalThis: any = (() => {
 })();
 
 type Builtin = Date | Function | Uint8Array | string | number | boolean | undefined;
+
 export type DeepPartial<T> = T extends Builtin
   ? T
   : T extends Array<infer U>
@@ -191,6 +192,11 @@ export type DeepPartial<T> = T extends Builtin
   ? { [K in keyof T]?: DeepPartial<T[K]> }
   : Partial<T>;
 
+type KeysOfUnion<T> = T extends T ? keyof T : never;
+export type Exact<P, I extends P> = P extends Builtin
+  ? P
+  : P & { [K in keyof P]: Exact<P[K], I[K]> } & Record<Exclude<keyof I, KeysOfUnion<P>>, never>;
+
 function longToNumber(long: Long): number {
   if (long.gt(Number.MAX_SAFE_INTEGER)) {
     throw new globalThis.Error('Value is larger than Number.MAX_SAFE_INTEGER');
diff --git a/integration/grpc-js/google/protobuf/wrappers.ts b/integration/grpc-js/google/protobuf/wrappers.ts
index 216285744..35b159990 100644
--- a/integration/grpc-js/google/protobuf/wrappers.ts
+++ b/integration/grpc-js/google/protobuf/wrappers.ts
@@ -134,7 +134,7 @@ export const DoubleValue = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<DoubleValue>): DoubleValue {
+  fromPartial<I extends Exact<DeepPartial<DoubleValue>, I>>(object: I): DoubleValue {
     const message = { ...baseDoubleValue } as DoubleValue;
     message.value = object.value ?? 0;
     return message;
@@ -181,7 +181,7 @@ export const FloatValue = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<FloatValue>): FloatValue {
+  fromPartial<I extends Exact<DeepPartial<FloatValue>, I>>(object: I): FloatValue {
     const message = { ...baseFloatValue } as FloatValue;
     message.value = object.value ?? 0;
     return message;
@@ -228,7 +228,7 @@ export const Int64Value = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Int64Value>): Int64Value {
+  fromPartial<I extends Exact<DeepPartial<Int64Value>, I>>(object: I): Int64Value {
     const message = { ...baseInt64Value } as Int64Value;
     message.value = object.value ?? 0;
     return message;
@@ -275,7 +275,7 @@ export const UInt64Value = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<UInt64Value>): UInt64Value {
+  fromPartial<I extends Exact<DeepPartial<UInt64Value>, I>>(object: I): UInt64Value {
     const message = { ...baseUInt64Value } as UInt64Value;
     message.value = object.value ?? 0;
     return message;
@@ -322,7 +322,7 @@ export const Int32Value = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Int32Value>): Int32Value {
+  fromPartial<I extends Exact<DeepPartial<Int32Value>, I>>(object: I): Int32Value {
     const message = { ...baseInt32Value } as Int32Value;
     message.value = object.value ?? 0;
     return message;
@@ -369,7 +369,7 @@ export const UInt32Value = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<UInt32Value>): UInt32Value {
+  fromPartial<I extends Exact<DeepPartial<UInt32Value>, I>>(object: I): UInt32Value {
     const message = { ...baseUInt32Value } as UInt32Value;
     message.value = object.value ?? 0;
     return message;
@@ -416,7 +416,7 @@ export const BoolValue = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<BoolValue>): BoolValue {
+  fromPartial<I extends Exact<DeepPartial<BoolValue>, I>>(object: I): BoolValue {
     const message = { ...baseBoolValue } as BoolValue;
     message.value = object.value ?? false;
     return message;
@@ -463,7 +463,7 @@ export const StringValue = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<StringValue>): StringValue {
+  fromPartial<I extends Exact<DeepPartial<StringValue>, I>>(object: I): StringValue {
     const message = { ...baseStringValue } as StringValue;
     message.value = object.value ?? '';
     return message;
@@ -513,7 +513,7 @@ export const BytesValue = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<BytesValue>): BytesValue {
+  fromPartial<I extends Exact<DeepPartial<BytesValue>, I>>(object: I): BytesValue {
     const message = { ...baseBytesValue } as BytesValue;
     message.value = object.value ?? new Uint8Array();
     return message;
@@ -553,6 +553,7 @@ function base64FromBytes(arr: Uint8Array): string {
 }
 
 type Builtin = Date | Function | Uint8Array | string | number | boolean | undefined;
+
 export type DeepPartial<T> = T extends Builtin
   ? T
   : T extends Array<infer U>
@@ -563,6 +564,11 @@ export type DeepPartial<T> = T extends Builtin
   ? { [K in keyof T]?: DeepPartial<T[K]> }
   : Partial<T>;
 
+type KeysOfUnion<T> = T extends T ? keyof T : never;
+export type Exact<P, I extends P> = P extends Builtin
+  ? P
+  : P & { [K in keyof P]: Exact<P[K], I[K]> } & Record<Exclude<keyof I, KeysOfUnion<P>>, never>;
+
 function longToNumber(long: Long): number {
   if (long.gt(Number.MAX_SAFE_INTEGER)) {
     throw new globalThis.Error('Value is larger than Number.MAX_SAFE_INTEGER');
diff --git a/integration/grpc-js/simple.ts b/integration/grpc-js/simple.ts
index 51193a12f..c8eb3ede9 100644
--- a/integration/grpc-js/simple.ts
+++ b/integration/grpc-js/simple.ts
@@ -81,7 +81,7 @@ export const TestMessage = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<TestMessage>): TestMessage {
+  fromPartial<I extends Exact<DeepPartial<TestMessage>, I>>(object: I): TestMessage {
     const message = { ...baseTestMessage } as TestMessage;
     message.timestamp = object.timestamp ?? undefined;
     return message;
@@ -622,6 +622,7 @@ export const TestClient = (makeGenericClientConstructor(TestService, 'simple.Tes
 };
 
 type Builtin = Date | Function | Uint8Array | string | number | boolean | undefined;
+
 export type DeepPartial<T> = T extends Builtin
   ? T
   : T extends Array<infer U>
@@ -632,6 +633,11 @@ export type DeepPartial<T> = T extends Builtin
   ? { [K in keyof T]?: DeepPartial<T[K]> }
   : Partial<T>;
 
+type KeysOfUnion<T> = T extends T ? keyof T : never;
+export type Exact<P, I extends P> = P extends Builtin
+  ? P
+  : P & { [K in keyof P]: Exact<P[K], I[K]> } & Record<Exclude<keyof I, KeysOfUnion<P>>, never>;
+
 function toTimestamp(date: Date): Timestamp {
   const seconds = date.getTime() / 1_000;
   const nanos = (date.getTime() % 1_000) * 1_000_000;
diff --git a/integration/grpc-web-go-server/example.ts b/integration/grpc-web-go-server/example.ts
index 9c45365aa..95f4a127f 100644
--- a/integration/grpc-web-go-server/example.ts
+++ b/integration/grpc-web-go-server/example.ts
@@ -140,7 +140,7 @@ export const DashFlash = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<DashFlash>): DashFlash {
+  fromPartial<I extends Exact<DeepPartial<DashFlash>, I>>(object: I): DashFlash {
     const message = { ...baseDashFlash } as DashFlash;
     message.msg = object.msg ?? '';
     message.type = object.type ?? 0;
@@ -211,14 +211,14 @@ export const DashUserSettingsState = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<DashUserSettingsState>): DashUserSettingsState {
+  fromPartial<I extends Exact<DeepPartial<DashUserSettingsState>, I>>(object: I): DashUserSettingsState {
     const message = { ...baseDashUserSettingsState } as DashUserSettingsState;
     message.email = object.email ?? '';
     message.urls =
       object.urls !== undefined && object.urls !== null
         ? DashUserSettingsState_URLs.fromPartial(object.urls)
         : undefined;
-    message.flashes = (object.flashes ?? []).map((e) => DashFlash.fromPartial(e));
+    message.flashes = object.flashes?.map((e) => DashFlash.fromPartial(e)) || [];
     return message;
   },
 };
@@ -273,7 +273,7 @@ export const DashUserSettingsState_URLs = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<DashUserSettingsState_URLs>): DashUserSettingsState_URLs {
+  fromPartial<I extends Exact<DeepPartial<DashUserSettingsState_URLs>, I>>(object: I): DashUserSettingsState_URLs {
     const message = { ...baseDashUserSettingsState_URLs } as DashUserSettingsState_URLs;
     message.connectGoogle = object.connectGoogle ?? '';
     message.connectGithub = object.connectGithub ?? '';
@@ -346,7 +346,7 @@ export const DashCred = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<DashCred>): DashCred {
+  fromPartial<I extends Exact<DeepPartial<DashCred>, I>>(object: I): DashCred {
     const message = { ...baseDashCred } as DashCred;
     message.description = object.description ?? '';
     message.metadata = object.metadata ?? '';
@@ -405,7 +405,7 @@ export const DashAPICredsCreateReq = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<DashAPICredsCreateReq>): DashAPICredsCreateReq {
+  fromPartial<I extends Exact<DeepPartial<DashAPICredsCreateReq>, I>>(object: I): DashAPICredsCreateReq {
     const message = { ...baseDashAPICredsCreateReq } as DashAPICredsCreateReq;
     message.description = object.description ?? '';
     message.metadata = object.metadata ?? '';
@@ -478,7 +478,7 @@ export const DashAPICredsUpdateReq = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<DashAPICredsUpdateReq>): DashAPICredsUpdateReq {
+  fromPartial<I extends Exact<DeepPartial<DashAPICredsUpdateReq>, I>>(object: I): DashAPICredsUpdateReq {
     const message = { ...baseDashAPICredsUpdateReq } as DashAPICredsUpdateReq;
     message.credSid = object.credSid ?? '';
     message.description = object.description ?? '';
@@ -536,7 +536,7 @@ export const DashAPICredsDeleteReq = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<DashAPICredsDeleteReq>): DashAPICredsDeleteReq {
+  fromPartial<I extends Exact<DeepPartial<DashAPICredsDeleteReq>, I>>(object: I): DashAPICredsDeleteReq {
     const message = { ...baseDashAPICredsDeleteReq } as DashAPICredsDeleteReq;
     message.credSid = object.credSid ?? '';
     message.id = object.id ?? '';
@@ -576,7 +576,7 @@ export const Empty = {
     return obj;
   },
 
-  fromPartial(_: DeepPartial<Empty>): Empty {
+  fromPartial<I extends Exact<DeepPartial<Empty>, I>>(_: I): Empty {
     const message = { ...baseEmpty } as Empty;
     return message;
   },
@@ -653,6 +653,7 @@ interface Rpc {
 }
 
 type Builtin = Date | Function | Uint8Array | string | number | boolean | undefined;
+
 export type DeepPartial<T> = T extends Builtin
   ? T
   : T extends Array<infer U>
@@ -663,6 +664,11 @@ export type DeepPartial<T> = T extends Builtin
   ? { [K in keyof T]?: DeepPartial<T[K]> }
   : Partial<T>;
 
+type KeysOfUnion<T> = T extends T ? keyof T : never;
+export type Exact<P, I extends P> = P extends Builtin
+  ? P
+  : P & { [K in keyof P]: Exact<P[K], I[K]> } & Record<Exclude<keyof I, KeysOfUnion<P>>, never>;
+
 // If you get a compile-error about 'Constructor<Long> and ... have no overlap',
 // add '--ts_proto_opt=esModuleInterop=true' as a flag when calling 'protoc'.
 if (util.Long !== Long) {
diff --git a/integration/grpc-web-no-streaming-observable/example.ts b/integration/grpc-web-no-streaming-observable/example.ts
index 9595cea8d..01695c187 100644
--- a/integration/grpc-web-no-streaming-observable/example.ts
+++ b/integration/grpc-web-no-streaming-observable/example.ts
@@ -118,7 +118,7 @@ export const DashFlash = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<DashFlash>): DashFlash {
+  fromPartial<I extends Exact<DeepPartial<DashFlash>, I>>(object: I): DashFlash {
     const message = { ...baseDashFlash } as DashFlash;
     message.msg = object.msg ?? '';
     message.type = object.type ?? 0;
@@ -189,14 +189,14 @@ export const DashUserSettingsState = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<DashUserSettingsState>): DashUserSettingsState {
+  fromPartial<I extends Exact<DeepPartial<DashUserSettingsState>, I>>(object: I): DashUserSettingsState {
     const message = { ...baseDashUserSettingsState } as DashUserSettingsState;
     message.email = object.email ?? '';
     message.urls =
       object.urls !== undefined && object.urls !== null
         ? DashUserSettingsState_URLs.fromPartial(object.urls)
         : undefined;
-    message.flashes = (object.flashes ?? []).map((e) => DashFlash.fromPartial(e));
+    message.flashes = object.flashes?.map((e) => DashFlash.fromPartial(e)) || [];
     return message;
   },
 };
@@ -251,7 +251,7 @@ export const DashUserSettingsState_URLs = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<DashUserSettingsState_URLs>): DashUserSettingsState_URLs {
+  fromPartial<I extends Exact<DeepPartial<DashUserSettingsState_URLs>, I>>(object: I): DashUserSettingsState_URLs {
     const message = { ...baseDashUserSettingsState_URLs } as DashUserSettingsState_URLs;
     message.connectGoogle = object.connectGoogle ?? '';
     message.connectGithub = object.connectGithub ?? '';
@@ -291,7 +291,7 @@ export const Empty = {
     return obj;
   },
 
-  fromPartial(_: DeepPartial<Empty>): Empty {
+  fromPartial<I extends Exact<DeepPartial<Empty>, I>>(_: I): Empty {
     const message = { ...baseEmpty } as Empty;
     return message;
   },
@@ -412,6 +412,7 @@ export class GrpcWebImpl {
 }
 
 type Builtin = Date | Function | Uint8Array | string | number | boolean | undefined;
+
 export type DeepPartial<T> = T extends Builtin
   ? T
   : T extends Array<infer U>
@@ -422,6 +423,11 @@ export type DeepPartial<T> = T extends Builtin
   ? { [K in keyof T]?: DeepPartial<T[K]> }
   : Partial<T>;
 
+type KeysOfUnion<T> = T extends T ? keyof T : never;
+export type Exact<P, I extends P> = P extends Builtin
+  ? P
+  : P & { [K in keyof P]: Exact<P[K], I[K]> } & Record<Exclude<keyof I, KeysOfUnion<P>>, never>;
+
 // If you get a compile-error about 'Constructor<Long> and ... have no overlap',
 // add '--ts_proto_opt=esModuleInterop=true' as a flag when calling 'protoc'.
 if (util.Long !== Long) {
diff --git a/integration/grpc-web-no-streaming/example.ts b/integration/grpc-web-no-streaming/example.ts
index 44a2bb82a..54f2f3f8d 100644
--- a/integration/grpc-web-no-streaming/example.ts
+++ b/integration/grpc-web-no-streaming/example.ts
@@ -116,7 +116,7 @@ export const DashFlash = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<DashFlash>): DashFlash {
+  fromPartial<I extends Exact<DeepPartial<DashFlash>, I>>(object: I): DashFlash {
     const message = { ...baseDashFlash } as DashFlash;
     message.msg = object.msg ?? '';
     message.type = object.type ?? 0;
@@ -187,14 +187,14 @@ export const DashUserSettingsState = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<DashUserSettingsState>): DashUserSettingsState {
+  fromPartial<I extends Exact<DeepPartial<DashUserSettingsState>, I>>(object: I): DashUserSettingsState {
     const message = { ...baseDashUserSettingsState } as DashUserSettingsState;
     message.email = object.email ?? '';
     message.urls =
       object.urls !== undefined && object.urls !== null
         ? DashUserSettingsState_URLs.fromPartial(object.urls)
         : undefined;
-    message.flashes = (object.flashes ?? []).map((e) => DashFlash.fromPartial(e));
+    message.flashes = object.flashes?.map((e) => DashFlash.fromPartial(e)) || [];
     return message;
   },
 };
@@ -249,7 +249,7 @@ export const DashUserSettingsState_URLs = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<DashUserSettingsState_URLs>): DashUserSettingsState_URLs {
+  fromPartial<I extends Exact<DeepPartial<DashUserSettingsState_URLs>, I>>(object: I): DashUserSettingsState_URLs {
     const message = { ...baseDashUserSettingsState_URLs } as DashUserSettingsState_URLs;
     message.connectGoogle = object.connectGoogle ?? '';
     message.connectGithub = object.connectGithub ?? '';
@@ -289,7 +289,7 @@ export const Empty = {
     return obj;
   },
 
-  fromPartial(_: DeepPartial<Empty>): Empty {
+  fromPartial<I extends Exact<DeepPartial<Empty>, I>>(_: I): Empty {
     const message = { ...baseEmpty } as Empty;
     return message;
   },
@@ -412,6 +412,7 @@ export class GrpcWebImpl {
 }
 
 type Builtin = Date | Function | Uint8Array | string | number | boolean | undefined;
+
 export type DeepPartial<T> = T extends Builtin
   ? T
   : T extends Array<infer U>
@@ -422,6 +423,11 @@ export type DeepPartial<T> = T extends Builtin
   ? { [K in keyof T]?: DeepPartial<T[K]> }
   : Partial<T>;
 
+type KeysOfUnion<T> = T extends T ? keyof T : never;
+export type Exact<P, I extends P> = P extends Builtin
+  ? P
+  : P & { [K in keyof P]: Exact<P[K], I[K]> } & Record<Exclude<keyof I, KeysOfUnion<P>>, never>;
+
 // If you get a compile-error about 'Constructor<Long> and ... have no overlap',
 // add '--ts_proto_opt=esModuleInterop=true' as a flag when calling 'protoc'.
 if (util.Long !== Long) {
diff --git a/integration/grpc-web/example.ts b/integration/grpc-web/example.ts
index 3c45cf699..35f814528 100644
--- a/integration/grpc-web/example.ts
+++ b/integration/grpc-web/example.ts
@@ -142,7 +142,7 @@ export const DashFlash = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<DashFlash>): DashFlash {
+  fromPartial<I extends Exact<DeepPartial<DashFlash>, I>>(object: I): DashFlash {
     const message = { ...baseDashFlash } as DashFlash;
     message.msg = object.msg ?? '';
     message.type = object.type ?? 0;
@@ -213,14 +213,14 @@ export const DashUserSettingsState = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<DashUserSettingsState>): DashUserSettingsState {
+  fromPartial<I extends Exact<DeepPartial<DashUserSettingsState>, I>>(object: I): DashUserSettingsState {
     const message = { ...baseDashUserSettingsState } as DashUserSettingsState;
     message.email = object.email ?? '';
     message.urls =
       object.urls !== undefined && object.urls !== null
         ? DashUserSettingsState_URLs.fromPartial(object.urls)
         : undefined;
-    message.flashes = (object.flashes ?? []).map((e) => DashFlash.fromPartial(e));
+    message.flashes = object.flashes?.map((e) => DashFlash.fromPartial(e)) || [];
     return message;
   },
 };
@@ -275,7 +275,7 @@ export const DashUserSettingsState_URLs = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<DashUserSettingsState_URLs>): DashUserSettingsState_URLs {
+  fromPartial<I extends Exact<DeepPartial<DashUserSettingsState_URLs>, I>>(object: I): DashUserSettingsState_URLs {
     const message = { ...baseDashUserSettingsState_URLs } as DashUserSettingsState_URLs;
     message.connectGoogle = object.connectGoogle ?? '';
     message.connectGithub = object.connectGithub ?? '';
@@ -348,7 +348,7 @@ export const DashCred = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<DashCred>): DashCred {
+  fromPartial<I extends Exact<DeepPartial<DashCred>, I>>(object: I): DashCred {
     const message = { ...baseDashCred } as DashCred;
     message.description = object.description ?? '';
     message.metadata = object.metadata ?? '';
@@ -407,7 +407,7 @@ export const DashAPICredsCreateReq = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<DashAPICredsCreateReq>): DashAPICredsCreateReq {
+  fromPartial<I extends Exact<DeepPartial<DashAPICredsCreateReq>, I>>(object: I): DashAPICredsCreateReq {
     const message = { ...baseDashAPICredsCreateReq } as DashAPICredsCreateReq;
     message.description = object.description ?? '';
     message.metadata = object.metadata ?? '';
@@ -480,7 +480,7 @@ export const DashAPICredsUpdateReq = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<DashAPICredsUpdateReq>): DashAPICredsUpdateReq {
+  fromPartial<I extends Exact<DeepPartial<DashAPICredsUpdateReq>, I>>(object: I): DashAPICredsUpdateReq {
     const message = { ...baseDashAPICredsUpdateReq } as DashAPICredsUpdateReq;
     message.credSid = object.credSid ?? '';
     message.description = object.description ?? '';
@@ -538,7 +538,7 @@ export const DashAPICredsDeleteReq = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<DashAPICredsDeleteReq>): DashAPICredsDeleteReq {
+  fromPartial<I extends Exact<DeepPartial<DashAPICredsDeleteReq>, I>>(object: I): DashAPICredsDeleteReq {
     const message = { ...baseDashAPICredsDeleteReq } as DashAPICredsDeleteReq;
     message.credSid = object.credSid ?? '';
     message.id = object.id ?? '';
@@ -578,7 +578,7 @@ export const Empty = {
     return obj;
   },
 
-  fromPartial(_: DeepPartial<Empty>): Empty {
+  fromPartial<I extends Exact<DeepPartial<Empty>, I>>(_: I): Empty {
     const message = { ...baseEmpty } as Empty;
     return message;
   },
@@ -872,6 +872,7 @@ export class GrpcWebImpl {
 }
 
 type Builtin = Date | Function | Uint8Array | string | number | boolean | undefined;
+
 export type DeepPartial<T> = T extends Builtin
   ? T
   : T extends Array<infer U>
@@ -882,6 +883,11 @@ export type DeepPartial<T> = T extends Builtin
   ? { [K in keyof T]?: DeepPartial<T[K]> }
   : Partial<T>;
 
+type KeysOfUnion<T> = T extends T ? keyof T : never;
+export type Exact<P, I extends P> = P extends Builtin
+  ? P
+  : P & { [K in keyof P]: Exact<P[K], I[K]> } & Record<Exclude<keyof I, KeysOfUnion<P>>, never>;
+
 // If you get a compile-error about 'Constructor<Long> and ... have no overlap',
 // add '--ts_proto_opt=esModuleInterop=true' as a flag when calling 'protoc'.
 if (util.Long !== Long) {
diff --git a/integration/lower-case-svc-methods/math.ts b/integration/lower-case-svc-methods/math.ts
index 3d3114e4e..734260076 100644
--- a/integration/lower-case-svc-methods/math.ts
+++ b/integration/lower-case-svc-methods/math.ts
@@ -67,7 +67,7 @@ export const NumPair = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<NumPair>): NumPair {
+  fromPartial<I extends Exact<DeepPartial<NumPair>, I>>(object: I): NumPair {
     const message = { ...baseNumPair } as NumPair;
     message.num1 = object.num1 ?? 0;
     message.num2 = object.num2 ?? 0;
@@ -115,7 +115,7 @@ export const NumSingle = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<NumSingle>): NumSingle {
+  fromPartial<I extends Exact<DeepPartial<NumSingle>, I>>(object: I): NumSingle {
     const message = { ...baseNumSingle } as NumSingle;
     message.num = object.num ?? 0;
     return message;
@@ -176,9 +176,9 @@ export const Numbers = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Numbers>): Numbers {
+  fromPartial<I extends Exact<DeepPartial<Numbers>, I>>(object: I): Numbers {
     const message = { ...baseNumbers } as Numbers;
-    message.num = (object.num ?? []).map((e) => e);
+    message.num = object.num?.map((e) => e) || [];
     return message;
   },
 };
@@ -244,6 +244,7 @@ export interface DataLoaders {
 }
 
 type Builtin = Date | Function | Uint8Array | string | number | boolean | undefined;
+
 export type DeepPartial<T> = T extends Builtin
   ? T
   : T extends Array<infer U>
@@ -254,6 +255,11 @@ export type DeepPartial<T> = T extends Builtin
   ? { [K in keyof T]?: DeepPartial<T[K]> }
   : Partial<T>;
 
+type KeysOfUnion<T> = T extends T ? keyof T : never;
+export type Exact<P, I extends P> = P extends Builtin
+  ? P
+  : P & { [K in keyof P]: Exact<P[K], I[K]> } & Record<Exclude<keyof I, KeysOfUnion<P>>, never>;
+
 // If you get a compile-error about 'Constructor<Long> and ... have no overlap',
 // add '--ts_proto_opt=esModuleInterop=true' as a flag when calling 'protoc'.
 if (util.Long !== Long) {
diff --git a/integration/no-proto-package/no-proto-package.ts b/integration/no-proto-package/no-proto-package.ts
index 2ebf4b84a..7939a0fac 100644
--- a/integration/no-proto-package/no-proto-package.ts
+++ b/integration/no-proto-package/no-proto-package.ts
@@ -52,7 +52,7 @@ export const User = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<User>): User {
+  fromPartial<I extends Exact<DeepPartial<User>, I>>(object: I): User {
     const message = { ...baseUser } as User;
     message.name = object.name ?? '';
     return message;
@@ -91,7 +91,7 @@ export const Empty = {
     return obj;
   },
 
-  fromPartial(_: DeepPartial<Empty>): Empty {
+  fromPartial<I extends Exact<DeepPartial<Empty>, I>>(_: I): Empty {
     const message = { ...baseEmpty } as Empty;
     return message;
   },
@@ -122,6 +122,7 @@ interface Rpc {
 }
 
 type Builtin = Date | Function | Uint8Array | string | number | boolean | undefined;
+
 export type DeepPartial<T> = T extends Builtin
   ? T
   : T extends Array<infer U>
@@ -132,6 +133,11 @@ export type DeepPartial<T> = T extends Builtin
   ? { [K in keyof T]?: DeepPartial<T[K]> }
   : Partial<T>;
 
+type KeysOfUnion<T> = T extends T ? keyof T : never;
+export type Exact<P, I extends P> = P extends Builtin
+  ? P
+  : P & { [K in keyof P]: Exact<P[K], I[K]> } & Record<Exclude<keyof I, KeysOfUnion<P>>, never>;
+
 // If you get a compile-error about 'Constructor<Long> and ... have no overlap',
 // add '--ts_proto_opt=esModuleInterop=true' as a flag when calling 'protoc'.
 if (util.Long !== Long) {
diff --git a/integration/oneof-properties/oneof.ts b/integration/oneof-properties/oneof.ts
index ba25e9a45..050d017e6 100644
--- a/integration/oneof-properties/oneof.ts
+++ b/integration/oneof-properties/oneof.ts
@@ -201,7 +201,7 @@ export const PleaseChoose = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<PleaseChoose>): PleaseChoose {
+  fromPartial<I extends Exact<DeepPartial<PleaseChoose>, I>>(object: I): PleaseChoose {
     const message = { ...basePleaseChoose } as PleaseChoose;
     message.name = object.name ?? '';
     message.aNumber = object.aNumber ?? undefined;
@@ -261,7 +261,7 @@ export const PleaseChoose_Submessage = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<PleaseChoose_Submessage>): PleaseChoose_Submessage {
+  fromPartial<I extends Exact<DeepPartial<PleaseChoose_Submessage>, I>>(object: I): PleaseChoose_Submessage {
     const message = { ...basePleaseChoose_Submessage } as PleaseChoose_Submessage;
     message.name = object.name ?? '';
     return message;
@@ -301,6 +301,7 @@ function base64FromBytes(arr: Uint8Array): string {
 }
 
 type Builtin = Date | Function | Uint8Array | string | number | boolean | undefined;
+
 export type DeepPartial<T> = T extends Builtin
   ? T
   : T extends Array<infer U>
@@ -311,6 +312,11 @@ export type DeepPartial<T> = T extends Builtin
   ? { [K in keyof T]?: DeepPartial<T[K]> }
   : Partial<T>;
 
+type KeysOfUnion<T> = T extends T ? keyof T : never;
+export type Exact<P, I extends P> = P extends Builtin
+  ? P
+  : P & { [K in keyof P]: Exact<P[K], I[K]> } & Record<Exclude<keyof I, KeysOfUnion<P>>, never>;
+
 // If you get a compile-error about 'Constructor<Long> and ... have no overlap',
 // add '--ts_proto_opt=esModuleInterop=true' as a flag when calling 'protoc'.
 if (util.Long !== Long) {
diff --git a/integration/oneof-unions/oneof.ts b/integration/oneof-unions/oneof.ts
index c4bb89be7..0b522ec26 100644
--- a/integration/oneof-unions/oneof.ts
+++ b/integration/oneof-unions/oneof.ts
@@ -225,7 +225,7 @@ export const PleaseChoose = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<PleaseChoose>): PleaseChoose {
+  fromPartial<I extends Exact<DeepPartial<PleaseChoose>, I>>(object: I): PleaseChoose {
     const message = { ...basePleaseChoose } as PleaseChoose;
     message.name = object.name ?? '';
     if (object.choice?.$case === 'aNumber' && object.choice?.aNumber !== undefined && object.choice?.aNumber !== null) {
@@ -317,7 +317,7 @@ export const PleaseChoose_Submessage = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<PleaseChoose_Submessage>): PleaseChoose_Submessage {
+  fromPartial<I extends Exact<DeepPartial<PleaseChoose_Submessage>, I>>(object: I): PleaseChoose_Submessage {
     const message = { ...basePleaseChoose_Submessage } as PleaseChoose_Submessage;
     message.name = object.name ?? '';
     return message;
@@ -372,7 +372,7 @@ export const SimpleButOptional = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<SimpleButOptional>): SimpleButOptional {
+  fromPartial<I extends Exact<DeepPartial<SimpleButOptional>, I>>(object: I): SimpleButOptional {
     const message = { ...baseSimpleButOptional } as SimpleButOptional;
     message.name = object.name ?? undefined;
     message.age = object.age ?? undefined;
@@ -413,6 +413,7 @@ function base64FromBytes(arr: Uint8Array): string {
 }
 
 type Builtin = Date | Function | Uint8Array | string | number | boolean | undefined;
+
 export type DeepPartial<T> = T extends Builtin
   ? T
   : T extends Array<infer U>
@@ -425,6 +426,11 @@ export type DeepPartial<T> = T extends Builtin
   ? { [K in keyof T]?: DeepPartial<T[K]> }
   : Partial<T>;
 
+type KeysOfUnion<T> = T extends T ? keyof T : never;
+export type Exact<P, I extends P> = P extends Builtin
+  ? P
+  : P & { [K in keyof P]: Exact<P[K], I[K]> } & Record<Exclude<keyof I, KeysOfUnion<P>>, never>;
+
 // If you get a compile-error about 'Constructor<Long> and ... have no overlap',
 // add '--ts_proto_opt=esModuleInterop=true' as a flag when calling 'protoc'.
 if (util.Long !== Long) {
diff --git a/integration/point/point.ts b/integration/point/point.ts
index b177a9983..065a2397f 100644
--- a/integration/point/point.ts
+++ b/integration/point/point.ts
@@ -62,7 +62,7 @@ export const Point = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Point>): Point {
+  fromPartial<I extends Exact<DeepPartial<Point>, I>>(object: I): Point {
     const message = { ...basePoint } as Point;
     message.lat = object.lat ?? 0;
     message.lng = object.lng ?? 0;
@@ -118,7 +118,7 @@ export const Area = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Area>): Area {
+  fromPartial<I extends Exact<DeepPartial<Area>, I>>(object: I): Area {
     const message = { ...baseArea } as Area;
     message.nw = object.nw !== undefined && object.nw !== null ? Point.fromPartial(object.nw) : undefined;
     message.se = object.se !== undefined && object.se !== null ? Point.fromPartial(object.se) : undefined;
@@ -127,6 +127,7 @@ export const Area = {
 };
 
 type Builtin = Date | Function | Uint8Array | string | number | boolean | undefined;
+
 export type DeepPartial<T> = T extends Builtin
   ? T
   : T extends Array<infer U>
@@ -137,6 +138,11 @@ export type DeepPartial<T> = T extends Builtin
   ? { [K in keyof T]?: DeepPartial<T[K]> }
   : Partial<T>;
 
+type KeysOfUnion<T> = T extends T ? keyof T : never;
+export type Exact<P, I extends P> = P extends Builtin
+  ? P
+  : P & { [K in keyof P]: Exact<P[K], I[K]> } & Record<Exclude<keyof I, KeysOfUnion<P>>, never>;
+
 // If you get a compile-error about 'Constructor<Long> and ... have no overlap',
 // add '--ts_proto_opt=esModuleInterop=true' as a flag when calling 'protoc'.
 if (util.Long !== Long) {
diff --git a/integration/return-observable/observable.ts b/integration/return-observable/observable.ts
index ea41954c1..c72522a30 100644
--- a/integration/return-observable/observable.ts
+++ b/integration/return-observable/observable.ts
@@ -54,7 +54,7 @@ export const ProduceRequest = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<ProduceRequest>): ProduceRequest {
+  fromPartial<I extends Exact<DeepPartial<ProduceRequest>, I>>(object: I): ProduceRequest {
     const message = { ...baseProduceRequest } as ProduceRequest;
     message.ingredients = object.ingredients ?? '';
     return message;
@@ -101,7 +101,7 @@ export const ProduceReply = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<ProduceReply>): ProduceReply {
+  fromPartial<I extends Exact<DeepPartial<ProduceReply>, I>>(object: I): ProduceReply {
     const message = { ...baseProduceReply } as ProduceReply;
     message.result = object.result ?? '';
     return message;
@@ -113,6 +113,7 @@ export interface Factory {
 }
 
 type Builtin = Date | Function | Uint8Array | string | number | boolean | undefined;
+
 export type DeepPartial<T> = T extends Builtin
   ? T
   : T extends Array<infer U>
@@ -123,6 +124,11 @@ export type DeepPartial<T> = T extends Builtin
   ? { [K in keyof T]?: DeepPartial<T[K]> }
   : Partial<T>;
 
+type KeysOfUnion<T> = T extends T ? keyof T : never;
+export type Exact<P, I extends P> = P extends Builtin
+  ? P
+  : P & { [K in keyof P]: Exact<P[K], I[K]> } & Record<Exclude<keyof I, KeysOfUnion<P>>, never>;
+
 // If you get a compile-error about 'Constructor<Long> and ... have no overlap',
 // add '--ts_proto_opt=esModuleInterop=true' as a flag when calling 'protoc'.
 if (util.Long !== Long) {
diff --git a/integration/simple-deprecated-fields/simple.ts b/integration/simple-deprecated-fields/simple.ts
index e4e09d731..66936d91a 100644
--- a/integration/simple-deprecated-fields/simple.ts
+++ b/integration/simple-deprecated-fields/simple.ts
@@ -107,7 +107,7 @@ export const Simple = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Simple>): Simple {
+  fromPartial<I extends Exact<DeepPartial<Simple>, I>>(object: I): Simple {
     const message = { ...baseSimple } as Simple;
     message.name = object.name ?? '';
     message.age = object.age ?? 0;
@@ -158,7 +158,7 @@ export const Child = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Child>): Child {
+  fromPartial<I extends Exact<DeepPartial<Child>, I>>(object: I): Child {
     const message = { ...baseChild } as Child;
     message.name = object.name ?? '';
     return message;
@@ -166,6 +166,7 @@ export const Child = {
 };
 
 type Builtin = Date | Function | Uint8Array | string | number | boolean | undefined;
+
 export type DeepPartial<T> = T extends Builtin
   ? T
   : T extends Array<infer U>
@@ -176,6 +177,11 @@ export type DeepPartial<T> = T extends Builtin
   ? { [K in keyof T]?: DeepPartial<T[K]> }
   : Partial<T>;
 
+type KeysOfUnion<T> = T extends T ? keyof T : never;
+export type Exact<P, I extends P> = P extends Builtin
+  ? P
+  : P & { [K in keyof P]: Exact<P[K], I[K]> } & Record<Exclude<keyof I, KeysOfUnion<P>>, never>;
+
 // If you get a compile-error about 'Constructor<Long> and ... have no overlap',
 // add '--ts_proto_opt=esModuleInterop=true' as a flag when calling 'protoc'.
 if (util.Long !== Long) {
diff --git a/integration/simple-esmodule-interop/simple.ts b/integration/simple-esmodule-interop/simple.ts
index f003ac4f7..6e71cb9ca 100644
--- a/integration/simple-esmodule-interop/simple.ts
+++ b/integration/simple-esmodule-interop/simple.ts
@@ -72,7 +72,7 @@ export const Simple = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Simple>): Simple {
+  fromPartial<I extends Exact<DeepPartial<Simple>, I>>(object: I): Simple {
     const message = { ...baseSimple } as Simple;
     message.name = object.name ?? '';
     message.age = object.age ?? 0;
@@ -221,7 +221,7 @@ export const Numbers = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Numbers>): Numbers {
+  fromPartial<I extends Exact<DeepPartial<Numbers>, I>>(object: I): Numbers {
     const message = { ...baseNumbers } as Numbers;
     message.double = object.double ?? 0;
     message.float = object.float ?? 0;
@@ -251,6 +251,7 @@ var globalThis: any = (() => {
 })();
 
 type Builtin = Date | Function | Uint8Array | string | number | boolean | undefined;
+
 export type DeepPartial<T> = T extends Builtin
   ? T
   : T extends Array<infer U>
@@ -261,6 +262,11 @@ export type DeepPartial<T> = T extends Builtin
   ? { [K in keyof T]?: DeepPartial<T[K]> }
   : Partial<T>;
 
+type KeysOfUnion<T> = T extends T ? keyof T : never;
+export type Exact<P, I extends P> = P extends Builtin
+  ? P
+  : P & { [K in keyof P]: Exact<P[K], I[K]> } & Record<Exclude<keyof I, KeysOfUnion<P>>, never>;
+
 function longToNumber(long: Long): number {
   if (long.gt(Number.MAX_SAFE_INTEGER)) {
     throw new globalThis.Error('Value is larger than Number.MAX_SAFE_INTEGER');
diff --git a/integration/simple-json-name/google/protobuf/timestamp.ts b/integration/simple-json-name/google/protobuf/timestamp.ts
index e4600a73e..0670c17fd 100644
--- a/integration/simple-json-name/google/protobuf/timestamp.ts
+++ b/integration/simple-json-name/google/protobuf/timestamp.ts
@@ -161,7 +161,7 @@ export const Timestamp = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Timestamp>): Timestamp {
+  fromPartial<I extends Exact<DeepPartial<Timestamp>, I>>(object: I): Timestamp {
     const message = { ...baseTimestamp } as Timestamp;
     message.seconds = object.seconds ?? 0;
     message.nanos = object.nanos ?? 0;
@@ -181,6 +181,7 @@ var globalThis: any = (() => {
 })();
 
 type Builtin = Date | Function | Uint8Array | string | number | boolean | undefined;
+
 export type DeepPartial<T> = T extends Builtin
   ? T
   : T extends Array<infer U>
@@ -191,6 +192,11 @@ export type DeepPartial<T> = T extends Builtin
   ? { [K in keyof T]?: DeepPartial<T[K]> }
   : Partial<T>;
 
+type KeysOfUnion<T> = T extends T ? keyof T : never;
+export type Exact<P, I extends P> = P extends Builtin
+  ? P
+  : P & { [K in keyof P]: Exact<P[K], I[K]> } & Record<Exclude<keyof I, KeysOfUnion<P>>, never>;
+
 function longToNumber(long: Long): number {
   if (long.gt(Number.MAX_SAFE_INTEGER)) {
     throw new globalThis.Error('Value is larger than Number.MAX_SAFE_INTEGER');
diff --git a/integration/simple-json-name/simple.ts b/integration/simple-json-name/simple.ts
index db9761249..3b9e779b3 100644
--- a/integration/simple-json-name/simple.ts
+++ b/integration/simple-json-name/simple.ts
@@ -68,7 +68,7 @@ export const Simple = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Simple>): Simple {
+  fromPartial<I extends Exact<DeepPartial<Simple>, I>>(object: I): Simple {
     const message = { ...baseSimple } as Simple;
     message.name = object.name ?? '';
     message.age = object.age ?? undefined;
@@ -78,6 +78,7 @@ export const Simple = {
 };
 
 type Builtin = Date | Function | Uint8Array | string | number | boolean | undefined;
+
 export type DeepPartial<T> = T extends Builtin
   ? T
   : T extends Array<infer U>
@@ -88,6 +89,11 @@ export type DeepPartial<T> = T extends Builtin
   ? { [K in keyof T]?: DeepPartial<T[K]> }
   : Partial<T>;
 
+type KeysOfUnion<T> = T extends T ? keyof T : never;
+export type Exact<P, I extends P> = P extends Builtin
+  ? P
+  : P & { [K in keyof P]: Exact<P[K], I[K]> } & Record<Exclude<keyof I, KeysOfUnion<P>>, never>;
+
 function toTimestamp(date: Date): Timestamp {
   const seconds = date.getTime() / 1_000;
   const nanos = (date.getTime() % 1_000) * 1_000_000;
diff --git a/integration/simple-long-string/google/protobuf/timestamp.ts b/integration/simple-long-string/google/protobuf/timestamp.ts
index 0fc344c57..1ef0034f3 100644
--- a/integration/simple-long-string/google/protobuf/timestamp.ts
+++ b/integration/simple-long-string/google/protobuf/timestamp.ts
@@ -161,7 +161,7 @@ export const Timestamp = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Timestamp>): Timestamp {
+  fromPartial<I extends Exact<DeepPartial<Timestamp>, I>>(object: I): Timestamp {
     const message = { ...baseTimestamp } as Timestamp;
     message.seconds = object.seconds ?? '0';
     message.nanos = object.nanos ?? 0;
@@ -170,6 +170,7 @@ export const Timestamp = {
 };
 
 type Builtin = Date | Function | Uint8Array | string | number | boolean | undefined;
+
 export type DeepPartial<T> = T extends Builtin
   ? T
   : T extends Array<infer U>
@@ -180,6 +181,11 @@ export type DeepPartial<T> = T extends Builtin
   ? { [K in keyof T]?: DeepPartial<T[K]> }
   : Partial<T>;
 
+type KeysOfUnion<T> = T extends T ? keyof T : never;
+export type Exact<P, I extends P> = P extends Builtin
+  ? P
+  : P & { [K in keyof P]: Exact<P[K], I[K]> } & Record<Exclude<keyof I, KeysOfUnion<P>>, never>;
+
 function longToString(long: Long) {
   return long.toString();
 }
diff --git a/integration/simple-long-string/google/protobuf/wrappers.ts b/integration/simple-long-string/google/protobuf/wrappers.ts
index 1be69752e..e2af04a95 100644
--- a/integration/simple-long-string/google/protobuf/wrappers.ts
+++ b/integration/simple-long-string/google/protobuf/wrappers.ts
@@ -134,7 +134,7 @@ export const DoubleValue = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<DoubleValue>): DoubleValue {
+  fromPartial<I extends Exact<DeepPartial<DoubleValue>, I>>(object: I): DoubleValue {
     const message = { ...baseDoubleValue } as DoubleValue;
     message.value = object.value ?? 0;
     return message;
@@ -181,7 +181,7 @@ export const FloatValue = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<FloatValue>): FloatValue {
+  fromPartial<I extends Exact<DeepPartial<FloatValue>, I>>(object: I): FloatValue {
     const message = { ...baseFloatValue } as FloatValue;
     message.value = object.value ?? 0;
     return message;
@@ -228,7 +228,7 @@ export const Int64Value = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Int64Value>): Int64Value {
+  fromPartial<I extends Exact<DeepPartial<Int64Value>, I>>(object: I): Int64Value {
     const message = { ...baseInt64Value } as Int64Value;
     message.value = object.value ?? '0';
     return message;
@@ -275,7 +275,7 @@ export const UInt64Value = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<UInt64Value>): UInt64Value {
+  fromPartial<I extends Exact<DeepPartial<UInt64Value>, I>>(object: I): UInt64Value {
     const message = { ...baseUInt64Value } as UInt64Value;
     message.value = object.value ?? '0';
     return message;
@@ -322,7 +322,7 @@ export const Int32Value = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Int32Value>): Int32Value {
+  fromPartial<I extends Exact<DeepPartial<Int32Value>, I>>(object: I): Int32Value {
     const message = { ...baseInt32Value } as Int32Value;
     message.value = object.value ?? 0;
     return message;
@@ -369,7 +369,7 @@ export const UInt32Value = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<UInt32Value>): UInt32Value {
+  fromPartial<I extends Exact<DeepPartial<UInt32Value>, I>>(object: I): UInt32Value {
     const message = { ...baseUInt32Value } as UInt32Value;
     message.value = object.value ?? 0;
     return message;
@@ -416,7 +416,7 @@ export const BoolValue = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<BoolValue>): BoolValue {
+  fromPartial<I extends Exact<DeepPartial<BoolValue>, I>>(object: I): BoolValue {
     const message = { ...baseBoolValue } as BoolValue;
     message.value = object.value ?? false;
     return message;
@@ -463,7 +463,7 @@ export const StringValue = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<StringValue>): StringValue {
+  fromPartial<I extends Exact<DeepPartial<StringValue>, I>>(object: I): StringValue {
     const message = { ...baseStringValue } as StringValue;
     message.value = object.value ?? '';
     return message;
@@ -513,7 +513,7 @@ export const BytesValue = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<BytesValue>): BytesValue {
+  fromPartial<I extends Exact<DeepPartial<BytesValue>, I>>(object: I): BytesValue {
     const message = { ...baseBytesValue } as BytesValue;
     message.value = object.value ?? new Uint8Array();
     return message;
@@ -553,6 +553,7 @@ function base64FromBytes(arr: Uint8Array): string {
 }
 
 type Builtin = Date | Function | Uint8Array | string | number | boolean | undefined;
+
 export type DeepPartial<T> = T extends Builtin
   ? T
   : T extends Array<infer U>
@@ -563,6 +564,11 @@ export type DeepPartial<T> = T extends Builtin
   ? { [K in keyof T]?: DeepPartial<T[K]> }
   : Partial<T>;
 
+type KeysOfUnion<T> = T extends T ? keyof T : never;
+export type Exact<P, I extends P> = P extends Builtin
+  ? P
+  : P & { [K in keyof P]: Exact<P[K], I[K]> } & Record<Exclude<keyof I, KeysOfUnion<P>>, never>;
+
 function longToString(long: Long) {
   return long.toString();
 }
diff --git a/integration/simple-long-string/simple.ts b/integration/simple-long-string/simple.ts
index a2cab3808..2136a5a19 100644
--- a/integration/simple-long-string/simple.ts
+++ b/integration/simple-long-string/simple.ts
@@ -181,7 +181,7 @@ export const Numbers = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Numbers>): Numbers {
+  fromPartial<I extends Exact<DeepPartial<Numbers>, I>>(object: I): Numbers {
     const message = { ...baseNumbers } as Numbers;
     message.double = object.double ?? 0;
     message.float = object.float ?? 0;
@@ -202,6 +202,7 @@ export const Numbers = {
 };
 
 type Builtin = Date | Function | Uint8Array | string | number | boolean | undefined;
+
 export type DeepPartial<T> = T extends Builtin
   ? T
   : T extends Array<infer U>
@@ -212,6 +213,11 @@ export type DeepPartial<T> = T extends Builtin
   ? { [K in keyof T]?: DeepPartial<T[K]> }
   : Partial<T>;
 
+type KeysOfUnion<T> = T extends T ? keyof T : never;
+export type Exact<P, I extends P> = P extends Builtin
+  ? P
+  : P & { [K in keyof P]: Exact<P[K], I[K]> } & Record<Exclude<keyof I, KeysOfUnion<P>>, never>;
+
 function toTimestamp(date: Date): Timestamp {
   const seconds = Math.trunc(date.getTime() / 1_000).toString();
   const nanos = (date.getTime() % 1_000) * 1_000_000;
diff --git a/integration/simple-long/google/protobuf/wrappers.ts b/integration/simple-long/google/protobuf/wrappers.ts
index 26ad3cd97..baaac22ba 100644
--- a/integration/simple-long/google/protobuf/wrappers.ts
+++ b/integration/simple-long/google/protobuf/wrappers.ts
@@ -134,7 +134,7 @@ export const DoubleValue = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<DoubleValue>): DoubleValue {
+  fromPartial<I extends Exact<DeepPartial<DoubleValue>, I>>(object: I): DoubleValue {
     const message = { ...baseDoubleValue } as DoubleValue;
     message.value = object.value ?? 0;
     return message;
@@ -181,7 +181,7 @@ export const FloatValue = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<FloatValue>): FloatValue {
+  fromPartial<I extends Exact<DeepPartial<FloatValue>, I>>(object: I): FloatValue {
     const message = { ...baseFloatValue } as FloatValue;
     message.value = object.value ?? 0;
     return message;
@@ -228,7 +228,7 @@ export const Int64Value = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Int64Value>): Int64Value {
+  fromPartial<I extends Exact<DeepPartial<Int64Value>, I>>(object: I): Int64Value {
     const message = { ...baseInt64Value } as Int64Value;
     message.value = object.value !== undefined && object.value !== null ? Long.fromValue(object.value) : Long.ZERO;
     return message;
@@ -275,7 +275,7 @@ export const UInt64Value = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<UInt64Value>): UInt64Value {
+  fromPartial<I extends Exact<DeepPartial<UInt64Value>, I>>(object: I): UInt64Value {
     const message = { ...baseUInt64Value } as UInt64Value;
     message.value = object.value !== undefined && object.value !== null ? Long.fromValue(object.value) : Long.UZERO;
     return message;
@@ -322,7 +322,7 @@ export const Int32Value = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Int32Value>): Int32Value {
+  fromPartial<I extends Exact<DeepPartial<Int32Value>, I>>(object: I): Int32Value {
     const message = { ...baseInt32Value } as Int32Value;
     message.value = object.value ?? 0;
     return message;
@@ -369,7 +369,7 @@ export const UInt32Value = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<UInt32Value>): UInt32Value {
+  fromPartial<I extends Exact<DeepPartial<UInt32Value>, I>>(object: I): UInt32Value {
     const message = { ...baseUInt32Value } as UInt32Value;
     message.value = object.value ?? 0;
     return message;
@@ -416,7 +416,7 @@ export const BoolValue = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<BoolValue>): BoolValue {
+  fromPartial<I extends Exact<DeepPartial<BoolValue>, I>>(object: I): BoolValue {
     const message = { ...baseBoolValue } as BoolValue;
     message.value = object.value ?? false;
     return message;
@@ -463,7 +463,7 @@ export const StringValue = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<StringValue>): StringValue {
+  fromPartial<I extends Exact<DeepPartial<StringValue>, I>>(object: I): StringValue {
     const message = { ...baseStringValue } as StringValue;
     message.value = object.value ?? '';
     return message;
@@ -513,7 +513,7 @@ export const BytesValue = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<BytesValue>): BytesValue {
+  fromPartial<I extends Exact<DeepPartial<BytesValue>, I>>(object: I): BytesValue {
     const message = { ...baseBytesValue } as BytesValue;
     message.value = object.value ?? new Uint8Array();
     return message;
@@ -553,6 +553,7 @@ function base64FromBytes(arr: Uint8Array): string {
 }
 
 type Builtin = Date | Function | Uint8Array | string | number | boolean | undefined;
+
 export type DeepPartial<T> = T extends Builtin
   ? T
   : T extends Long
@@ -565,6 +566,11 @@ export type DeepPartial<T> = T extends Builtin
   ? { [K in keyof T]?: DeepPartial<T[K]> }
   : Partial<T>;
 
+type KeysOfUnion<T> = T extends T ? keyof T : never;
+export type Exact<P, I extends P> = P extends Builtin
+  ? P
+  : P & { [K in keyof P]: Exact<P[K], I[K]> } & Record<Exclude<keyof I, KeysOfUnion<P>>, never>;
+
 // If you get a compile-error about 'Constructor<Long> and ... have no overlap',
 // add '--ts_proto_opt=esModuleInterop=true' as a flag when calling 'protoc'.
 if (util.Long !== Long) {
diff --git a/integration/simple-long/simple.ts b/integration/simple-long/simple.ts
index 87561d012..2dd555206 100644
--- a/integration/simple-long/simple.ts
+++ b/integration/simple-long/simple.ts
@@ -144,15 +144,15 @@ export const SimpleWithWrappers = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<SimpleWithWrappers>): SimpleWithWrappers {
+  fromPartial<I extends Exact<DeepPartial<SimpleWithWrappers>, I>>(object: I): SimpleWithWrappers {
     const message = { ...baseSimpleWithWrappers } as SimpleWithWrappers;
     message.name = object.name ?? undefined;
     message.age = object.age ?? undefined;
     message.enabled = object.enabled ?? undefined;
     message.bananas =
       object.bananas !== undefined && object.bananas !== null ? Long.fromValue(object.bananas) : undefined;
-    message.coins = (object.coins ?? []).map((e) => e);
-    message.snacks = (object.snacks ?? []).map((e) => e);
+    message.coins = object.coins?.map((e) => e) || [];
+    message.snacks = object.snacks?.map((e) => e) || [];
     return message;
   },
 };
@@ -258,7 +258,7 @@ export const SimpleWithMap = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<SimpleWithMap>): SimpleWithMap {
+  fromPartial<I extends Exact<DeepPartial<SimpleWithMap>, I>>(object: I): SimpleWithMap {
     const message = { ...baseSimpleWithMap } as SimpleWithMap;
     message.nameLookup = Object.entries(object.nameLookup ?? {}).reduce<{ [key: string]: string }>(
       (acc, [key, value]) => {
@@ -339,7 +339,9 @@ export const SimpleWithMap_NameLookupEntry = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<SimpleWithMap_NameLookupEntry>): SimpleWithMap_NameLookupEntry {
+  fromPartial<I extends Exact<DeepPartial<SimpleWithMap_NameLookupEntry>, I>>(
+    object: I
+  ): SimpleWithMap_NameLookupEntry {
     const message = { ...baseSimpleWithMap_NameLookupEntry } as SimpleWithMap_NameLookupEntry;
     message.key = object.key ?? '';
     message.value = object.value ?? '';
@@ -395,7 +397,7 @@ export const SimpleWithMap_IntLookupEntry = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<SimpleWithMap_IntLookupEntry>): SimpleWithMap_IntLookupEntry {
+  fromPartial<I extends Exact<DeepPartial<SimpleWithMap_IntLookupEntry>, I>>(object: I): SimpleWithMap_IntLookupEntry {
     const message = { ...baseSimpleWithMap_IntLookupEntry } as SimpleWithMap_IntLookupEntry;
     message.key = object.key ?? 0;
     message.value = object.value ?? 0;
@@ -451,7 +453,9 @@ export const SimpleWithMap_LongLookupEntry = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<SimpleWithMap_LongLookupEntry>): SimpleWithMap_LongLookupEntry {
+  fromPartial<I extends Exact<DeepPartial<SimpleWithMap_LongLookupEntry>, I>>(
+    object: I
+  ): SimpleWithMap_LongLookupEntry {
     const message = { ...baseSimpleWithMap_LongLookupEntry } as SimpleWithMap_LongLookupEntry;
     message.key = object.key ?? '';
     message.value = object.value !== undefined && object.value !== null ? Long.fromValue(object.value) : Long.ZERO;
@@ -626,7 +630,7 @@ export const Numbers = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Numbers>): Numbers {
+  fromPartial<I extends Exact<DeepPartial<Numbers>, I>>(object: I): Numbers {
     const message = { ...baseNumbers } as Numbers;
     message.double = object.double ?? 0;
     message.float = object.float ?? 0;
@@ -642,12 +646,13 @@ export const Numbers = {
     message.sfixed32 = object.sfixed32 ?? 0;
     message.sfixed64 =
       object.sfixed64 !== undefined && object.sfixed64 !== null ? Long.fromValue(object.sfixed64) : Long.ZERO;
-    message.manyUint64 = (object.manyUint64 ?? []).map((e) => Long.fromValue(e));
+    message.manyUint64 = object.manyUint64?.map((e) => Long.fromValue(e)) || [];
     return message;
   },
 };
 
 type Builtin = Date | Function | Uint8Array | string | number | boolean | undefined;
+
 export type DeepPartial<T> = T extends Builtin
   ? T
   : T extends Long
@@ -660,6 +665,11 @@ export type DeepPartial<T> = T extends Builtin
   ? { [K in keyof T]?: DeepPartial<T[K]> }
   : Partial<T>;
 
+type KeysOfUnion<T> = T extends T ? keyof T : never;
+export type Exact<P, I extends P> = P extends Builtin
+  ? P
+  : P & { [K in keyof P]: Exact<P[K], I[K]> } & Record<Exclude<keyof I, KeysOfUnion<P>>, never>;
+
 // If you get a compile-error about 'Constructor<Long> and ... have no overlap',
 // add '--ts_proto_opt=esModuleInterop=true' as a flag when calling 'protoc'.
 if (util.Long !== Long) {
diff --git a/integration/simple-optionals/google/protobuf/timestamp.ts b/integration/simple-optionals/google/protobuf/timestamp.ts
index e4600a73e..0670c17fd 100644
--- a/integration/simple-optionals/google/protobuf/timestamp.ts
+++ b/integration/simple-optionals/google/protobuf/timestamp.ts
@@ -161,7 +161,7 @@ export const Timestamp = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Timestamp>): Timestamp {
+  fromPartial<I extends Exact<DeepPartial<Timestamp>, I>>(object: I): Timestamp {
     const message = { ...baseTimestamp } as Timestamp;
     message.seconds = object.seconds ?? 0;
     message.nanos = object.nanos ?? 0;
@@ -181,6 +181,7 @@ var globalThis: any = (() => {
 })();
 
 type Builtin = Date | Function | Uint8Array | string | number | boolean | undefined;
+
 export type DeepPartial<T> = T extends Builtin
   ? T
   : T extends Array<infer U>
@@ -191,6 +192,11 @@ export type DeepPartial<T> = T extends Builtin
   ? { [K in keyof T]?: DeepPartial<T[K]> }
   : Partial<T>;
 
+type KeysOfUnion<T> = T extends T ? keyof T : never;
+export type Exact<P, I extends P> = P extends Builtin
+  ? P
+  : P & { [K in keyof P]: Exact<P[K], I[K]> } & Record<Exclude<keyof I, KeysOfUnion<P>>, never>;
+
 function longToNumber(long: Long): number {
   if (long.gt(Number.MAX_SAFE_INTEGER)) {
     throw new globalThis.Error('Value is larger than Number.MAX_SAFE_INTEGER');
diff --git a/integration/simple-optionals/google/protobuf/wrappers.ts b/integration/simple-optionals/google/protobuf/wrappers.ts
index 216285744..35b159990 100644
--- a/integration/simple-optionals/google/protobuf/wrappers.ts
+++ b/integration/simple-optionals/google/protobuf/wrappers.ts
@@ -134,7 +134,7 @@ export const DoubleValue = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<DoubleValue>): DoubleValue {
+  fromPartial<I extends Exact<DeepPartial<DoubleValue>, I>>(object: I): DoubleValue {
     const message = { ...baseDoubleValue } as DoubleValue;
     message.value = object.value ?? 0;
     return message;
@@ -181,7 +181,7 @@ export const FloatValue = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<FloatValue>): FloatValue {
+  fromPartial<I extends Exact<DeepPartial<FloatValue>, I>>(object: I): FloatValue {
     const message = { ...baseFloatValue } as FloatValue;
     message.value = object.value ?? 0;
     return message;
@@ -228,7 +228,7 @@ export const Int64Value = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Int64Value>): Int64Value {
+  fromPartial<I extends Exact<DeepPartial<Int64Value>, I>>(object: I): Int64Value {
     const message = { ...baseInt64Value } as Int64Value;
     message.value = object.value ?? 0;
     return message;
@@ -275,7 +275,7 @@ export const UInt64Value = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<UInt64Value>): UInt64Value {
+  fromPartial<I extends Exact<DeepPartial<UInt64Value>, I>>(object: I): UInt64Value {
     const message = { ...baseUInt64Value } as UInt64Value;
     message.value = object.value ?? 0;
     return message;
@@ -322,7 +322,7 @@ export const Int32Value = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Int32Value>): Int32Value {
+  fromPartial<I extends Exact<DeepPartial<Int32Value>, I>>(object: I): Int32Value {
     const message = { ...baseInt32Value } as Int32Value;
     message.value = object.value ?? 0;
     return message;
@@ -369,7 +369,7 @@ export const UInt32Value = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<UInt32Value>): UInt32Value {
+  fromPartial<I extends Exact<DeepPartial<UInt32Value>, I>>(object: I): UInt32Value {
     const message = { ...baseUInt32Value } as UInt32Value;
     message.value = object.value ?? 0;
     return message;
@@ -416,7 +416,7 @@ export const BoolValue = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<BoolValue>): BoolValue {
+  fromPartial<I extends Exact<DeepPartial<BoolValue>, I>>(object: I): BoolValue {
     const message = { ...baseBoolValue } as BoolValue;
     message.value = object.value ?? false;
     return message;
@@ -463,7 +463,7 @@ export const StringValue = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<StringValue>): StringValue {
+  fromPartial<I extends Exact<DeepPartial<StringValue>, I>>(object: I): StringValue {
     const message = { ...baseStringValue } as StringValue;
     message.value = object.value ?? '';
     return message;
@@ -513,7 +513,7 @@ export const BytesValue = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<BytesValue>): BytesValue {
+  fromPartial<I extends Exact<DeepPartial<BytesValue>, I>>(object: I): BytesValue {
     const message = { ...baseBytesValue } as BytesValue;
     message.value = object.value ?? new Uint8Array();
     return message;
@@ -553,6 +553,7 @@ function base64FromBytes(arr: Uint8Array): string {
 }
 
 type Builtin = Date | Function | Uint8Array | string | number | boolean | undefined;
+
 export type DeepPartial<T> = T extends Builtin
   ? T
   : T extends Array<infer U>
@@ -563,6 +564,11 @@ export type DeepPartial<T> = T extends Builtin
   ? { [K in keyof T]?: DeepPartial<T[K]> }
   : Partial<T>;
 
+type KeysOfUnion<T> = T extends T ? keyof T : never;
+export type Exact<P, I extends P> = P extends Builtin
+  ? P
+  : P & { [K in keyof P]: Exact<P[K], I[K]> } & Record<Exclude<keyof I, KeysOfUnion<P>>, never>;
+
 function longToNumber(long: Long): number {
   if (long.gt(Number.MAX_SAFE_INTEGER)) {
     throw new globalThis.Error('Value is larger than Number.MAX_SAFE_INTEGER');
diff --git a/integration/simple-optionals/import_dir/thing.ts b/integration/simple-optionals/import_dir/thing.ts
index 9dc4871d5..a1c6d81cf 100644
--- a/integration/simple-optionals/import_dir/thing.ts
+++ b/integration/simple-optionals/import_dir/thing.ts
@@ -50,7 +50,7 @@ export const ImportedThing = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<ImportedThing>): ImportedThing {
+  fromPartial<I extends Exact<DeepPartial<ImportedThing>, I>>(object: I): ImportedThing {
     const message = { ...baseImportedThing } as ImportedThing;
     message.createdAt = object.createdAt ?? undefined;
     return message;
@@ -58,6 +58,7 @@ export const ImportedThing = {
 };
 
 type Builtin = Date | Function | Uint8Array | string | number | boolean | undefined;
+
 export type DeepPartial<T> = T extends Builtin
   ? T
   : T extends Array<infer U>
@@ -68,6 +69,11 @@ export type DeepPartial<T> = T extends Builtin
   ? { [K in keyof T]?: DeepPartial<T[K]> }
   : Partial<T>;
 
+type KeysOfUnion<T> = T extends T ? keyof T : never;
+export type Exact<P, I extends P> = P extends Builtin
+  ? P
+  : P & { [K in keyof P]: Exact<P[K], I[K]> } & Record<Exclude<keyof I, KeysOfUnion<P>>, never>;
+
 function toTimestamp(date: Date): Timestamp {
   const seconds = date.getTime() / 1_000;
   const nanos = (date.getTime() % 1_000) * 1_000_000;
diff --git a/integration/simple-optionals/simple.ts b/integration/simple-optionals/simple.ts
index 6108c6ad8..7d4bf0b3f 100644
--- a/integration/simple-optionals/simple.ts
+++ b/integration/simple-optionals/simple.ts
@@ -387,17 +387,17 @@ export const Simple = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Simple>): Simple {
+  fromPartial<I extends Exact<DeepPartial<Simple>, I>>(object: I): Simple {
     const message = { ...baseSimple } as Simple;
     message.name = object.name ?? '';
     message.age = object.age ?? 0;
     message.createdAt = object.createdAt ?? undefined;
     message.child = object.child !== undefined && object.child !== null ? Child.fromPartial(object.child) : undefined;
     message.state = object.state ?? 0;
-    message.grandChildren = (object.grandChildren ?? []).map((e) => Child.fromPartial(e));
-    message.coins = (object.coins ?? []).map((e) => e);
-    message.snacks = (object.snacks ?? []).map((e) => e);
-    message.oldStates = (object.oldStates ?? []).map((e) => e);
+    message.grandChildren = object.grandChildren?.map((e) => Child.fromPartial(e)) || [];
+    message.coins = object.coins?.map((e) => e) || [];
+    message.snacks = object.snacks?.map((e) => e) || [];
+    message.oldStates = object.oldStates?.map((e) => e) || [];
     message.thing =
       object.thing !== undefined && object.thing !== null ? ImportedThing.fromPartial(object.thing) : undefined;
     return message;
@@ -452,7 +452,7 @@ export const Child = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Child>): Child {
+  fromPartial<I extends Exact<DeepPartial<Child>, I>>(object: I): Child {
     const message = { ...baseChild } as Child;
     message.name = object.name ?? '';
     message.type = object.type ?? 0;
@@ -520,7 +520,7 @@ export const Nested = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Nested>): Nested {
+  fromPartial<I extends Exact<DeepPartial<Nested>, I>>(object: I): Nested {
     const message = { ...baseNested } as Nested;
     message.name = object.name ?? '';
     message.message =
@@ -584,7 +584,7 @@ export const Nested_InnerMessage = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Nested_InnerMessage>): Nested_InnerMessage {
+  fromPartial<I extends Exact<DeepPartial<Nested_InnerMessage>, I>>(object: I): Nested_InnerMessage {
     const message = { ...baseNested_InnerMessage } as Nested_InnerMessage;
     message.name = object.name ?? '';
     message.deep =
@@ -635,7 +635,9 @@ export const Nested_InnerMessage_DeepMessage = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Nested_InnerMessage_DeepMessage>): Nested_InnerMessage_DeepMessage {
+  fromPartial<I extends Exact<DeepPartial<Nested_InnerMessage_DeepMessage>, I>>(
+    object: I
+  ): Nested_InnerMessage_DeepMessage {
     const message = { ...baseNested_InnerMessage_DeepMessage } as Nested_InnerMessage_DeepMessage;
     message.name = object.name ?? '';
     return message;
@@ -690,7 +692,7 @@ export const OneOfMessage = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<OneOfMessage>): OneOfMessage {
+  fromPartial<I extends Exact<DeepPartial<OneOfMessage>, I>>(object: I): OneOfMessage {
     const message = { ...baseOneOfMessage } as OneOfMessage;
     message.first = object.first ?? undefined;
     message.last = object.last ?? undefined;
@@ -780,13 +782,13 @@ export const SimpleWithWrappers = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<SimpleWithWrappers>): SimpleWithWrappers {
+  fromPartial<I extends Exact<DeepPartial<SimpleWithWrappers>, I>>(object: I): SimpleWithWrappers {
     const message = { ...baseSimpleWithWrappers } as SimpleWithWrappers;
     message.name = object.name ?? undefined;
     message.age = object.age ?? undefined;
     message.enabled = object.enabled ?? undefined;
-    message.coins = (object.coins ?? []).map((e) => e);
-    message.snacks = (object.snacks ?? []).map((e) => e);
+    message.coins = object.coins?.map((e) => e) || [];
+    message.snacks = object.snacks?.map((e) => e) || [];
     return message;
   },
 };
@@ -831,7 +833,7 @@ export const Entity = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Entity>): Entity {
+  fromPartial<I extends Exact<DeepPartial<Entity>, I>>(object: I): Entity {
     const message = { ...baseEntity } as Entity;
     message.id = object.id ?? 0;
     return message;
@@ -939,7 +941,7 @@ export const SimpleWithMap = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<SimpleWithMap>): SimpleWithMap {
+  fromPartial<I extends Exact<DeepPartial<SimpleWithMap>, I>>(object: I): SimpleWithMap {
     const message = { ...baseSimpleWithMap } as SimpleWithMap;
     message.entitiesById = Object.entries(object.entitiesById ?? {}).reduce<{ [key: number]: Entity }>(
       (acc, [key, value]) => {
@@ -1020,7 +1022,9 @@ export const SimpleWithMap_EntitiesByIdEntry = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<SimpleWithMap_EntitiesByIdEntry>): SimpleWithMap_EntitiesByIdEntry {
+  fromPartial<I extends Exact<DeepPartial<SimpleWithMap_EntitiesByIdEntry>, I>>(
+    object: I
+  ): SimpleWithMap_EntitiesByIdEntry {
     const message = { ...baseSimpleWithMap_EntitiesByIdEntry } as SimpleWithMap_EntitiesByIdEntry;
     message.key = object.key ?? 0;
     message.value = object.value !== undefined && object.value !== null ? Entity.fromPartial(object.value) : undefined;
@@ -1076,7 +1080,9 @@ export const SimpleWithMap_NameLookupEntry = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<SimpleWithMap_NameLookupEntry>): SimpleWithMap_NameLookupEntry {
+  fromPartial<I extends Exact<DeepPartial<SimpleWithMap_NameLookupEntry>, I>>(
+    object: I
+  ): SimpleWithMap_NameLookupEntry {
     const message = { ...baseSimpleWithMap_NameLookupEntry } as SimpleWithMap_NameLookupEntry;
     message.key = object.key ?? '';
     message.value = object.value ?? '';
@@ -1132,7 +1138,7 @@ export const SimpleWithMap_IntLookupEntry = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<SimpleWithMap_IntLookupEntry>): SimpleWithMap_IntLookupEntry {
+  fromPartial<I extends Exact<DeepPartial<SimpleWithMap_IntLookupEntry>, I>>(object: I): SimpleWithMap_IntLookupEntry {
     const message = { ...baseSimpleWithMap_IntLookupEntry } as SimpleWithMap_IntLookupEntry;
     message.key = object.key ?? 0;
     message.value = object.value ?? 0;
@@ -1195,7 +1201,7 @@ export const SimpleWithSnakeCaseMap = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<SimpleWithSnakeCaseMap>): SimpleWithSnakeCaseMap {
+  fromPartial<I extends Exact<DeepPartial<SimpleWithSnakeCaseMap>, I>>(object: I): SimpleWithSnakeCaseMap {
     const message = { ...baseSimpleWithSnakeCaseMap } as SimpleWithSnakeCaseMap;
     message.entitiesById = Object.entries(object.entitiesById ?? {}).reduce<{ [key: number]: Entity }>(
       (acc, [key, value]) => {
@@ -1258,7 +1264,9 @@ export const SimpleWithSnakeCaseMap_EntitiesByIdEntry = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<SimpleWithSnakeCaseMap_EntitiesByIdEntry>): SimpleWithSnakeCaseMap_EntitiesByIdEntry {
+  fromPartial<I extends Exact<DeepPartial<SimpleWithSnakeCaseMap_EntitiesByIdEntry>, I>>(
+    object: I
+  ): SimpleWithSnakeCaseMap_EntitiesByIdEntry {
     const message = { ...baseSimpleWithSnakeCaseMap_EntitiesByIdEntry } as SimpleWithSnakeCaseMap_EntitiesByIdEntry;
     message.key = object.key ?? 0;
     message.value = object.value !== undefined && object.value !== null ? Entity.fromPartial(object.value) : undefined;
@@ -1306,7 +1314,7 @@ export const PingRequest = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<PingRequest>): PingRequest {
+  fromPartial<I extends Exact<DeepPartial<PingRequest>, I>>(object: I): PingRequest {
     const message = { ...basePingRequest } as PingRequest;
     message.input = object.input ?? '';
     return message;
@@ -1353,7 +1361,7 @@ export const PingResponse = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<PingResponse>): PingResponse {
+  fromPartial<I extends Exact<DeepPartial<PingResponse>, I>>(object: I): PingResponse {
     const message = { ...basePingResponse } as PingResponse;
     message.output = object.output ?? '';
     return message;
@@ -1501,7 +1509,7 @@ export const Numbers = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Numbers>): Numbers {
+  fromPartial<I extends Exact<DeepPartial<Numbers>, I>>(object: I): Numbers {
     const message = { ...baseNumbers } as Numbers;
     message.double = object.double ?? 0;
     message.float = object.float ?? 0;
@@ -1552,6 +1560,7 @@ var globalThis: any = (() => {
 })();
 
 type Builtin = Date | Function | Uint8Array | string | number | boolean | undefined;
+
 export type DeepPartial<T> = T extends Builtin
   ? T
   : T extends Array<infer U>
@@ -1562,6 +1571,11 @@ export type DeepPartial<T> = T extends Builtin
   ? { [K in keyof T]?: DeepPartial<T[K]> }
   : Partial<T>;
 
+type KeysOfUnion<T> = T extends T ? keyof T : never;
+export type Exact<P, I extends P> = P extends Builtin
+  ? P
+  : P & { [K in keyof P]: Exact<P[K], I[K]> } & Record<Exclude<keyof I, KeysOfUnion<P>>, never>;
+
 function toTimestamp(date: Date): Timestamp {
   const seconds = date.getTime() / 1_000;
   const nanos = (date.getTime() % 1_000) * 1_000_000;
diff --git a/integration/simple-optionals/thing.ts b/integration/simple-optionals/thing.ts
index 2ce036f8c..6f19102e9 100644
--- a/integration/simple-optionals/thing.ts
+++ b/integration/simple-optionals/thing.ts
@@ -50,7 +50,7 @@ export const ImportedThing = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<ImportedThing>): ImportedThing {
+  fromPartial<I extends Exact<DeepPartial<ImportedThing>, I>>(object: I): ImportedThing {
     const message = { ...baseImportedThing } as ImportedThing;
     message.createdAt = object.createdAt ?? undefined;
     return message;
@@ -58,6 +58,7 @@ export const ImportedThing = {
 };
 
 type Builtin = Date | Function | Uint8Array | string | number | boolean | undefined;
+
 export type DeepPartial<T> = T extends Builtin
   ? T
   : T extends Array<infer U>
@@ -68,6 +69,11 @@ export type DeepPartial<T> = T extends Builtin
   ? { [K in keyof T]?: DeepPartial<T[K]> }
   : Partial<T>;
 
+type KeysOfUnion<T> = T extends T ? keyof T : never;
+export type Exact<P, I extends P> = P extends Builtin
+  ? P
+  : P & { [K in keyof P]: Exact<P[K], I[K]> } & Record<Exclude<keyof I, KeysOfUnion<P>>, never>;
+
 function toTimestamp(date: Date): Timestamp {
   const seconds = date.getTime() / 1_000;
   const nanos = (date.getTime() % 1_000) * 1_000_000;
diff --git a/integration/simple-proto2/simple.ts b/integration/simple-proto2/simple.ts
index a02b86c7c..88faab1db 100644
--- a/integration/simple-proto2/simple.ts
+++ b/integration/simple-proto2/simple.ts
@@ -80,7 +80,7 @@ export const Issue56 = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Issue56>): Issue56 {
+  fromPartial<I extends Exact<DeepPartial<Issue56>, I>>(object: I): Issue56 {
     const message = { ...baseIssue56 } as Issue56;
     message.test = object.test ?? 1;
     return message;
@@ -88,6 +88,7 @@ export const Issue56 = {
 };
 
 type Builtin = Date | Function | Uint8Array | string | number | boolean | undefined;
+
 export type DeepPartial<T> = T extends Builtin
   ? T
   : T extends Array<infer U>
@@ -98,6 +99,11 @@ export type DeepPartial<T> = T extends Builtin
   ? { [K in keyof T]?: DeepPartial<T[K]> }
   : Partial<T>;
 
+type KeysOfUnion<T> = T extends T ? keyof T : never;
+export type Exact<P, I extends P> = P extends Builtin
+  ? P
+  : P & { [K in keyof P]: Exact<P[K], I[K]> } & Record<Exclude<keyof I, KeysOfUnion<P>>, never>;
+
 // If you get a compile-error about 'Constructor<Long> and ... have no overlap',
 // add '--ts_proto_opt=esModuleInterop=true' as a flag when calling 'protoc'.
 if (util.Long !== Long) {
diff --git a/integration/simple-snake/google/protobuf/timestamp.ts b/integration/simple-snake/google/protobuf/timestamp.ts
index e4600a73e..0670c17fd 100644
--- a/integration/simple-snake/google/protobuf/timestamp.ts
+++ b/integration/simple-snake/google/protobuf/timestamp.ts
@@ -161,7 +161,7 @@ export const Timestamp = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Timestamp>): Timestamp {
+  fromPartial<I extends Exact<DeepPartial<Timestamp>, I>>(object: I): Timestamp {
     const message = { ...baseTimestamp } as Timestamp;
     message.seconds = object.seconds ?? 0;
     message.nanos = object.nanos ?? 0;
@@ -181,6 +181,7 @@ var globalThis: any = (() => {
 })();
 
 type Builtin = Date | Function | Uint8Array | string | number | boolean | undefined;
+
 export type DeepPartial<T> = T extends Builtin
   ? T
   : T extends Array<infer U>
@@ -191,6 +192,11 @@ export type DeepPartial<T> = T extends Builtin
   ? { [K in keyof T]?: DeepPartial<T[K]> }
   : Partial<T>;
 
+type KeysOfUnion<T> = T extends T ? keyof T : never;
+export type Exact<P, I extends P> = P extends Builtin
+  ? P
+  : P & { [K in keyof P]: Exact<P[K], I[K]> } & Record<Exclude<keyof I, KeysOfUnion<P>>, never>;
+
 function longToNumber(long: Long): number {
   if (long.gt(Number.MAX_SAFE_INTEGER)) {
     throw new globalThis.Error('Value is larger than Number.MAX_SAFE_INTEGER');
diff --git a/integration/simple-snake/google/protobuf/wrappers.ts b/integration/simple-snake/google/protobuf/wrappers.ts
index 216285744..35b159990 100644
--- a/integration/simple-snake/google/protobuf/wrappers.ts
+++ b/integration/simple-snake/google/protobuf/wrappers.ts
@@ -134,7 +134,7 @@ export const DoubleValue = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<DoubleValue>): DoubleValue {
+  fromPartial<I extends Exact<DeepPartial<DoubleValue>, I>>(object: I): DoubleValue {
     const message = { ...baseDoubleValue } as DoubleValue;
     message.value = object.value ?? 0;
     return message;
@@ -181,7 +181,7 @@ export const FloatValue = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<FloatValue>): FloatValue {
+  fromPartial<I extends Exact<DeepPartial<FloatValue>, I>>(object: I): FloatValue {
     const message = { ...baseFloatValue } as FloatValue;
     message.value = object.value ?? 0;
     return message;
@@ -228,7 +228,7 @@ export const Int64Value = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Int64Value>): Int64Value {
+  fromPartial<I extends Exact<DeepPartial<Int64Value>, I>>(object: I): Int64Value {
     const message = { ...baseInt64Value } as Int64Value;
     message.value = object.value ?? 0;
     return message;
@@ -275,7 +275,7 @@ export const UInt64Value = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<UInt64Value>): UInt64Value {
+  fromPartial<I extends Exact<DeepPartial<UInt64Value>, I>>(object: I): UInt64Value {
     const message = { ...baseUInt64Value } as UInt64Value;
     message.value = object.value ?? 0;
     return message;
@@ -322,7 +322,7 @@ export const Int32Value = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Int32Value>): Int32Value {
+  fromPartial<I extends Exact<DeepPartial<Int32Value>, I>>(object: I): Int32Value {
     const message = { ...baseInt32Value } as Int32Value;
     message.value = object.value ?? 0;
     return message;
@@ -369,7 +369,7 @@ export const UInt32Value = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<UInt32Value>): UInt32Value {
+  fromPartial<I extends Exact<DeepPartial<UInt32Value>, I>>(object: I): UInt32Value {
     const message = { ...baseUInt32Value } as UInt32Value;
     message.value = object.value ?? 0;
     return message;
@@ -416,7 +416,7 @@ export const BoolValue = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<BoolValue>): BoolValue {
+  fromPartial<I extends Exact<DeepPartial<BoolValue>, I>>(object: I): BoolValue {
     const message = { ...baseBoolValue } as BoolValue;
     message.value = object.value ?? false;
     return message;
@@ -463,7 +463,7 @@ export const StringValue = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<StringValue>): StringValue {
+  fromPartial<I extends Exact<DeepPartial<StringValue>, I>>(object: I): StringValue {
     const message = { ...baseStringValue } as StringValue;
     message.value = object.value ?? '';
     return message;
@@ -513,7 +513,7 @@ export const BytesValue = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<BytesValue>): BytesValue {
+  fromPartial<I extends Exact<DeepPartial<BytesValue>, I>>(object: I): BytesValue {
     const message = { ...baseBytesValue } as BytesValue;
     message.value = object.value ?? new Uint8Array();
     return message;
@@ -553,6 +553,7 @@ function base64FromBytes(arr: Uint8Array): string {
 }
 
 type Builtin = Date | Function | Uint8Array | string | number | boolean | undefined;
+
 export type DeepPartial<T> = T extends Builtin
   ? T
   : T extends Array<infer U>
@@ -563,6 +564,11 @@ export type DeepPartial<T> = T extends Builtin
   ? { [K in keyof T]?: DeepPartial<T[K]> }
   : Partial<T>;
 
+type KeysOfUnion<T> = T extends T ? keyof T : never;
+export type Exact<P, I extends P> = P extends Builtin
+  ? P
+  : P & { [K in keyof P]: Exact<P[K], I[K]> } & Record<Exclude<keyof I, KeysOfUnion<P>>, never>;
+
 function longToNumber(long: Long): number {
   if (long.gt(Number.MAX_SAFE_INTEGER)) {
     throw new globalThis.Error('Value is larger than Number.MAX_SAFE_INTEGER');
diff --git a/integration/simple-snake/import_dir/thing.ts b/integration/simple-snake/import_dir/thing.ts
index 3a013304a..a5e21f0c5 100644
--- a/integration/simple-snake/import_dir/thing.ts
+++ b/integration/simple-snake/import_dir/thing.ts
@@ -50,7 +50,7 @@ export const ImportedThing = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<ImportedThing>): ImportedThing {
+  fromPartial<I extends Exact<DeepPartial<ImportedThing>, I>>(object: I): ImportedThing {
     const message = { ...baseImportedThing } as ImportedThing;
     message.created_at = object.created_at ?? undefined;
     return message;
@@ -58,6 +58,7 @@ export const ImportedThing = {
 };
 
 type Builtin = Date | Function | Uint8Array | string | number | boolean | undefined;
+
 export type DeepPartial<T> = T extends Builtin
   ? T
   : T extends Array<infer U>
@@ -68,6 +69,11 @@ export type DeepPartial<T> = T extends Builtin
   ? { [K in keyof T]?: DeepPartial<T[K]> }
   : Partial<T>;
 
+type KeysOfUnion<T> = T extends T ? keyof T : never;
+export type Exact<P, I extends P> = P extends Builtin
+  ? P
+  : P & { [K in keyof P]: Exact<P[K], I[K]> } & Record<Exclude<keyof I, KeysOfUnion<P>>, never>;
+
 function toTimestamp(date: Date): Timestamp {
   const seconds = date.getTime() / 1_000;
   const nanos = (date.getTime() % 1_000) * 1_000_000;
diff --git a/integration/simple-snake/simple.ts b/integration/simple-snake/simple.ts
index ca2844a71..2f1d77fe9 100644
--- a/integration/simple-snake/simple.ts
+++ b/integration/simple-snake/simple.ts
@@ -387,17 +387,17 @@ export const Simple = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Simple>): Simple {
+  fromPartial<I extends Exact<DeepPartial<Simple>, I>>(object: I): Simple {
     const message = { ...baseSimple } as Simple;
     message.name = object.name ?? '';
     message.age = object.age ?? 0;
     message.created_at = object.created_at ?? undefined;
     message.child = object.child !== undefined && object.child !== null ? Child.fromPartial(object.child) : undefined;
     message.state = object.state ?? 0;
-    message.grand_children = (object.grand_children ?? []).map((e) => Child.fromPartial(e));
-    message.coins = (object.coins ?? []).map((e) => e);
-    message.snacks = (object.snacks ?? []).map((e) => e);
-    message.old_states = (object.old_states ?? []).map((e) => e);
+    message.grand_children = object.grand_children?.map((e) => Child.fromPartial(e)) || [];
+    message.coins = object.coins?.map((e) => e) || [];
+    message.snacks = object.snacks?.map((e) => e) || [];
+    message.old_states = object.old_states?.map((e) => e) || [];
     message.thing =
       object.thing !== undefined && object.thing !== null ? ImportedThing.fromPartial(object.thing) : undefined;
     return message;
@@ -452,7 +452,7 @@ export const Child = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Child>): Child {
+  fromPartial<I extends Exact<DeepPartial<Child>, I>>(object: I): Child {
     const message = { ...baseChild } as Child;
     message.name = object.name ?? '';
     message.type = object.type ?? 0;
@@ -520,7 +520,7 @@ export const Nested = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Nested>): Nested {
+  fromPartial<I extends Exact<DeepPartial<Nested>, I>>(object: I): Nested {
     const message = { ...baseNested } as Nested;
     message.name = object.name ?? '';
     message.message =
@@ -584,7 +584,7 @@ export const Nested_InnerMessage = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Nested_InnerMessage>): Nested_InnerMessage {
+  fromPartial<I extends Exact<DeepPartial<Nested_InnerMessage>, I>>(object: I): Nested_InnerMessage {
     const message = { ...baseNested_InnerMessage } as Nested_InnerMessage;
     message.name = object.name ?? '';
     message.deep =
@@ -635,7 +635,9 @@ export const Nested_InnerMessage_DeepMessage = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Nested_InnerMessage_DeepMessage>): Nested_InnerMessage_DeepMessage {
+  fromPartial<I extends Exact<DeepPartial<Nested_InnerMessage_DeepMessage>, I>>(
+    object: I
+  ): Nested_InnerMessage_DeepMessage {
     const message = { ...baseNested_InnerMessage_DeepMessage } as Nested_InnerMessage_DeepMessage;
     message.name = object.name ?? '';
     return message;
@@ -690,7 +692,7 @@ export const OneOfMessage = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<OneOfMessage>): OneOfMessage {
+  fromPartial<I extends Exact<DeepPartial<OneOfMessage>, I>>(object: I): OneOfMessage {
     const message = { ...baseOneOfMessage } as OneOfMessage;
     message.first = object.first ?? undefined;
     message.last = object.last ?? undefined;
@@ -780,13 +782,13 @@ export const SimpleWithWrappers = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<SimpleWithWrappers>): SimpleWithWrappers {
+  fromPartial<I extends Exact<DeepPartial<SimpleWithWrappers>, I>>(object: I): SimpleWithWrappers {
     const message = { ...baseSimpleWithWrappers } as SimpleWithWrappers;
     message.name = object.name ?? undefined;
     message.age = object.age ?? undefined;
     message.enabled = object.enabled ?? undefined;
-    message.coins = (object.coins ?? []).map((e) => e);
-    message.snacks = (object.snacks ?? []).map((e) => e);
+    message.coins = object.coins?.map((e) => e) || [];
+    message.snacks = object.snacks?.map((e) => e) || [];
     return message;
   },
 };
@@ -831,7 +833,7 @@ export const Entity = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Entity>): Entity {
+  fromPartial<I extends Exact<DeepPartial<Entity>, I>>(object: I): Entity {
     const message = { ...baseEntity } as Entity;
     message.id = object.id ?? 0;
     return message;
@@ -939,7 +941,7 @@ export const SimpleWithMap = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<SimpleWithMap>): SimpleWithMap {
+  fromPartial<I extends Exact<DeepPartial<SimpleWithMap>, I>>(object: I): SimpleWithMap {
     const message = { ...baseSimpleWithMap } as SimpleWithMap;
     message.entitiesById = Object.entries(object.entitiesById ?? {}).reduce<{ [key: number]: Entity }>(
       (acc, [key, value]) => {
@@ -1020,7 +1022,9 @@ export const SimpleWithMap_EntitiesByIdEntry = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<SimpleWithMap_EntitiesByIdEntry>): SimpleWithMap_EntitiesByIdEntry {
+  fromPartial<I extends Exact<DeepPartial<SimpleWithMap_EntitiesByIdEntry>, I>>(
+    object: I
+  ): SimpleWithMap_EntitiesByIdEntry {
     const message = { ...baseSimpleWithMap_EntitiesByIdEntry } as SimpleWithMap_EntitiesByIdEntry;
     message.key = object.key ?? 0;
     message.value = object.value !== undefined && object.value !== null ? Entity.fromPartial(object.value) : undefined;
@@ -1076,7 +1080,9 @@ export const SimpleWithMap_NameLookupEntry = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<SimpleWithMap_NameLookupEntry>): SimpleWithMap_NameLookupEntry {
+  fromPartial<I extends Exact<DeepPartial<SimpleWithMap_NameLookupEntry>, I>>(
+    object: I
+  ): SimpleWithMap_NameLookupEntry {
     const message = { ...baseSimpleWithMap_NameLookupEntry } as SimpleWithMap_NameLookupEntry;
     message.key = object.key ?? '';
     message.value = object.value ?? '';
@@ -1132,7 +1138,7 @@ export const SimpleWithMap_IntLookupEntry = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<SimpleWithMap_IntLookupEntry>): SimpleWithMap_IntLookupEntry {
+  fromPartial<I extends Exact<DeepPartial<SimpleWithMap_IntLookupEntry>, I>>(object: I): SimpleWithMap_IntLookupEntry {
     const message = { ...baseSimpleWithMap_IntLookupEntry } as SimpleWithMap_IntLookupEntry;
     message.key = object.key ?? 0;
     message.value = object.value ?? 0;
@@ -1195,7 +1201,7 @@ export const SimpleWithSnakeCaseMap = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<SimpleWithSnakeCaseMap>): SimpleWithSnakeCaseMap {
+  fromPartial<I extends Exact<DeepPartial<SimpleWithSnakeCaseMap>, I>>(object: I): SimpleWithSnakeCaseMap {
     const message = { ...baseSimpleWithSnakeCaseMap } as SimpleWithSnakeCaseMap;
     message.entities_by_id = Object.entries(object.entities_by_id ?? {}).reduce<{ [key: number]: Entity }>(
       (acc, [key, value]) => {
@@ -1258,7 +1264,9 @@ export const SimpleWithSnakeCaseMap_EntitiesByIdEntry = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<SimpleWithSnakeCaseMap_EntitiesByIdEntry>): SimpleWithSnakeCaseMap_EntitiesByIdEntry {
+  fromPartial<I extends Exact<DeepPartial<SimpleWithSnakeCaseMap_EntitiesByIdEntry>, I>>(
+    object: I
+  ): SimpleWithSnakeCaseMap_EntitiesByIdEntry {
     const message = { ...baseSimpleWithSnakeCaseMap_EntitiesByIdEntry } as SimpleWithSnakeCaseMap_EntitiesByIdEntry;
     message.key = object.key ?? 0;
     message.value = object.value !== undefined && object.value !== null ? Entity.fromPartial(object.value) : undefined;
@@ -1306,7 +1314,7 @@ export const PingRequest = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<PingRequest>): PingRequest {
+  fromPartial<I extends Exact<DeepPartial<PingRequest>, I>>(object: I): PingRequest {
     const message = { ...basePingRequest } as PingRequest;
     message.input = object.input ?? '';
     return message;
@@ -1353,7 +1361,7 @@ export const PingResponse = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<PingResponse>): PingResponse {
+  fromPartial<I extends Exact<DeepPartial<PingResponse>, I>>(object: I): PingResponse {
     const message = { ...basePingResponse } as PingResponse;
     message.output = object.output ?? '';
     return message;
@@ -1501,7 +1509,7 @@ export const Numbers = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Numbers>): Numbers {
+  fromPartial<I extends Exact<DeepPartial<Numbers>, I>>(object: I): Numbers {
     const message = { ...baseNumbers } as Numbers;
     message.double = object.double ?? 0;
     message.float = object.float ?? 0;
@@ -1552,6 +1560,7 @@ var globalThis: any = (() => {
 })();
 
 type Builtin = Date | Function | Uint8Array | string | number | boolean | undefined;
+
 export type DeepPartial<T> = T extends Builtin
   ? T
   : T extends Array<infer U>
@@ -1562,6 +1571,11 @@ export type DeepPartial<T> = T extends Builtin
   ? { [K in keyof T]?: DeepPartial<T[K]> }
   : Partial<T>;
 
+type KeysOfUnion<T> = T extends T ? keyof T : never;
+export type Exact<P, I extends P> = P extends Builtin
+  ? P
+  : P & { [K in keyof P]: Exact<P[K], I[K]> } & Record<Exclude<keyof I, KeysOfUnion<P>>, never>;
+
 function toTimestamp(date: Date): Timestamp {
   const seconds = date.getTime() / 1_000;
   const nanos = (date.getTime() % 1_000) * 1_000_000;
diff --git a/integration/simple-string-enums/simple.ts b/integration/simple-string-enums/simple.ts
index 655d8d239..41b0b1ee3 100644
--- a/integration/simple-string-enums/simple.ts
+++ b/integration/simple-string-enums/simple.ts
@@ -132,16 +132,17 @@ export const Simple = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Simple>): Simple {
+  fromPartial<I extends Exact<DeepPartial<Simple>, I>>(object: I): Simple {
     const message = { ...baseSimple } as Simple;
     message.name = object.name ?? '';
     message.state = object.state ?? StateEnum.UNKNOWN;
-    message.states = (object.states ?? []).map((e) => e);
+    message.states = object.states?.map((e) => e) || [];
     return message;
   },
 };
 
 type Builtin = Date | Function | Uint8Array | string | number | boolean | undefined;
+
 export type DeepPartial<T> = T extends Builtin
   ? T
   : T extends Array<infer U>
@@ -152,6 +153,11 @@ export type DeepPartial<T> = T extends Builtin
   ? { [K in keyof T]?: DeepPartial<T[K]> }
   : Partial<T>;
 
+type KeysOfUnion<T> = T extends T ? keyof T : never;
+export type Exact<P, I extends P> = P extends Builtin
+  ? P
+  : P & { [K in keyof P]: Exact<P[K], I[K]> } & Record<Exclude<keyof I, KeysOfUnion<P>>, never>;
+
 // If you get a compile-error about 'Constructor<Long> and ... have no overlap',
 // add '--ts_proto_opt=esModuleInterop=true' as a flag when calling 'protoc'.
 if (util.Long !== Long) {
diff --git a/integration/simple-unrecognized-enum/google/protobuf/timestamp.ts b/integration/simple-unrecognized-enum/google/protobuf/timestamp.ts
index e4600a73e..0670c17fd 100644
--- a/integration/simple-unrecognized-enum/google/protobuf/timestamp.ts
+++ b/integration/simple-unrecognized-enum/google/protobuf/timestamp.ts
@@ -161,7 +161,7 @@ export const Timestamp = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Timestamp>): Timestamp {
+  fromPartial<I extends Exact<DeepPartial<Timestamp>, I>>(object: I): Timestamp {
     const message = { ...baseTimestamp } as Timestamp;
     message.seconds = object.seconds ?? 0;
     message.nanos = object.nanos ?? 0;
@@ -181,6 +181,7 @@ var globalThis: any = (() => {
 })();
 
 type Builtin = Date | Function | Uint8Array | string | number | boolean | undefined;
+
 export type DeepPartial<T> = T extends Builtin
   ? T
   : T extends Array<infer U>
@@ -191,6 +192,11 @@ export type DeepPartial<T> = T extends Builtin
   ? { [K in keyof T]?: DeepPartial<T[K]> }
   : Partial<T>;
 
+type KeysOfUnion<T> = T extends T ? keyof T : never;
+export type Exact<P, I extends P> = P extends Builtin
+  ? P
+  : P & { [K in keyof P]: Exact<P[K], I[K]> } & Record<Exclude<keyof I, KeysOfUnion<P>>, never>;
+
 function longToNumber(long: Long): number {
   if (long.gt(Number.MAX_SAFE_INTEGER)) {
     throw new globalThis.Error('Value is larger than Number.MAX_SAFE_INTEGER');
diff --git a/integration/simple-unrecognized-enum/google/protobuf/wrappers.ts b/integration/simple-unrecognized-enum/google/protobuf/wrappers.ts
index 216285744..35b159990 100644
--- a/integration/simple-unrecognized-enum/google/protobuf/wrappers.ts
+++ b/integration/simple-unrecognized-enum/google/protobuf/wrappers.ts
@@ -134,7 +134,7 @@ export const DoubleValue = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<DoubleValue>): DoubleValue {
+  fromPartial<I extends Exact<DeepPartial<DoubleValue>, I>>(object: I): DoubleValue {
     const message = { ...baseDoubleValue } as DoubleValue;
     message.value = object.value ?? 0;
     return message;
@@ -181,7 +181,7 @@ export const FloatValue = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<FloatValue>): FloatValue {
+  fromPartial<I extends Exact<DeepPartial<FloatValue>, I>>(object: I): FloatValue {
     const message = { ...baseFloatValue } as FloatValue;
     message.value = object.value ?? 0;
     return message;
@@ -228,7 +228,7 @@ export const Int64Value = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Int64Value>): Int64Value {
+  fromPartial<I extends Exact<DeepPartial<Int64Value>, I>>(object: I): Int64Value {
     const message = { ...baseInt64Value } as Int64Value;
     message.value = object.value ?? 0;
     return message;
@@ -275,7 +275,7 @@ export const UInt64Value = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<UInt64Value>): UInt64Value {
+  fromPartial<I extends Exact<DeepPartial<UInt64Value>, I>>(object: I): UInt64Value {
     const message = { ...baseUInt64Value } as UInt64Value;
     message.value = object.value ?? 0;
     return message;
@@ -322,7 +322,7 @@ export const Int32Value = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Int32Value>): Int32Value {
+  fromPartial<I extends Exact<DeepPartial<Int32Value>, I>>(object: I): Int32Value {
     const message = { ...baseInt32Value } as Int32Value;
     message.value = object.value ?? 0;
     return message;
@@ -369,7 +369,7 @@ export const UInt32Value = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<UInt32Value>): UInt32Value {
+  fromPartial<I extends Exact<DeepPartial<UInt32Value>, I>>(object: I): UInt32Value {
     const message = { ...baseUInt32Value } as UInt32Value;
     message.value = object.value ?? 0;
     return message;
@@ -416,7 +416,7 @@ export const BoolValue = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<BoolValue>): BoolValue {
+  fromPartial<I extends Exact<DeepPartial<BoolValue>, I>>(object: I): BoolValue {
     const message = { ...baseBoolValue } as BoolValue;
     message.value = object.value ?? false;
     return message;
@@ -463,7 +463,7 @@ export const StringValue = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<StringValue>): StringValue {
+  fromPartial<I extends Exact<DeepPartial<StringValue>, I>>(object: I): StringValue {
     const message = { ...baseStringValue } as StringValue;
     message.value = object.value ?? '';
     return message;
@@ -513,7 +513,7 @@ export const BytesValue = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<BytesValue>): BytesValue {
+  fromPartial<I extends Exact<DeepPartial<BytesValue>, I>>(object: I): BytesValue {
     const message = { ...baseBytesValue } as BytesValue;
     message.value = object.value ?? new Uint8Array();
     return message;
@@ -553,6 +553,7 @@ function base64FromBytes(arr: Uint8Array): string {
 }
 
 type Builtin = Date | Function | Uint8Array | string | number | boolean | undefined;
+
 export type DeepPartial<T> = T extends Builtin
   ? T
   : T extends Array<infer U>
@@ -563,6 +564,11 @@ export type DeepPartial<T> = T extends Builtin
   ? { [K in keyof T]?: DeepPartial<T[K]> }
   : Partial<T>;
 
+type KeysOfUnion<T> = T extends T ? keyof T : never;
+export type Exact<P, I extends P> = P extends Builtin
+  ? P
+  : P & { [K in keyof P]: Exact<P[K], I[K]> } & Record<Exclude<keyof I, KeysOfUnion<P>>, never>;
+
 function longToNumber(long: Long): number {
   if (long.gt(Number.MAX_SAFE_INTEGER)) {
     throw new globalThis.Error('Value is larger than Number.MAX_SAFE_INTEGER');
diff --git a/integration/simple-unrecognized-enum/import_dir/thing.ts b/integration/simple-unrecognized-enum/import_dir/thing.ts
index 276e91e85..6a1771dcc 100644
--- a/integration/simple-unrecognized-enum/import_dir/thing.ts
+++ b/integration/simple-unrecognized-enum/import_dir/thing.ts
@@ -50,7 +50,7 @@ export const ImportedThing = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<ImportedThing>): ImportedThing {
+  fromPartial<I extends Exact<DeepPartial<ImportedThing>, I>>(object: I): ImportedThing {
     const message = { ...baseImportedThing } as ImportedThing;
     message.createdAt = object.createdAt ?? undefined;
     return message;
@@ -58,6 +58,7 @@ export const ImportedThing = {
 };
 
 type Builtin = Date | Function | Uint8Array | string | number | boolean | undefined;
+
 export type DeepPartial<T> = T extends Builtin
   ? T
   : T extends Array<infer U>
@@ -68,6 +69,11 @@ export type DeepPartial<T> = T extends Builtin
   ? { [K in keyof T]?: DeepPartial<T[K]> }
   : Partial<T>;
 
+type KeysOfUnion<T> = T extends T ? keyof T : never;
+export type Exact<P, I extends P> = P extends Builtin
+  ? P
+  : P & { [K in keyof P]: Exact<P[K], I[K]> } & Record<Exclude<keyof I, KeysOfUnion<P>>, never>;
+
 function toTimestamp(date: Date): Timestamp {
   const seconds = date.getTime() / 1_000;
   const nanos = (date.getTime() % 1_000) * 1_000_000;
diff --git a/integration/simple-unrecognized-enum/simple.ts b/integration/simple-unrecognized-enum/simple.ts
index d5d6ac01b..9cd1b6cc1 100644
--- a/integration/simple-unrecognized-enum/simple.ts
+++ b/integration/simple-unrecognized-enum/simple.ts
@@ -378,17 +378,17 @@ export const Simple = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Simple>): Simple {
+  fromPartial<I extends Exact<DeepPartial<Simple>, I>>(object: I): Simple {
     const message = { ...baseSimple } as Simple;
     message.name = object.name ?? '';
     message.age = object.age ?? 0;
     message.createdAt = object.createdAt ?? undefined;
     message.child = object.child !== undefined && object.child !== null ? Child.fromPartial(object.child) : undefined;
     message.state = object.state ?? 0;
-    message.grandChildren = (object.grandChildren ?? []).map((e) => Child.fromPartial(e));
-    message.coins = (object.coins ?? []).map((e) => e);
-    message.snacks = (object.snacks ?? []).map((e) => e);
-    message.oldStates = (object.oldStates ?? []).map((e) => e);
+    message.grandChildren = object.grandChildren?.map((e) => Child.fromPartial(e)) || [];
+    message.coins = object.coins?.map((e) => e) || [];
+    message.snacks = object.snacks?.map((e) => e) || [];
+    message.oldStates = object.oldStates?.map((e) => e) || [];
     message.thing =
       object.thing !== undefined && object.thing !== null ? ImportedThing.fromPartial(object.thing) : undefined;
     return message;
@@ -443,7 +443,7 @@ export const Child = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Child>): Child {
+  fromPartial<I extends Exact<DeepPartial<Child>, I>>(object: I): Child {
     const message = { ...baseChild } as Child;
     message.name = object.name ?? '';
     message.type = object.type ?? 0;
@@ -511,7 +511,7 @@ export const Nested = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Nested>): Nested {
+  fromPartial<I extends Exact<DeepPartial<Nested>, I>>(object: I): Nested {
     const message = { ...baseNested } as Nested;
     message.name = object.name ?? '';
     message.message =
@@ -575,7 +575,7 @@ export const Nested_InnerMessage = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Nested_InnerMessage>): Nested_InnerMessage {
+  fromPartial<I extends Exact<DeepPartial<Nested_InnerMessage>, I>>(object: I): Nested_InnerMessage {
     const message = { ...baseNested_InnerMessage } as Nested_InnerMessage;
     message.name = object.name ?? '';
     message.deep =
@@ -626,7 +626,9 @@ export const Nested_InnerMessage_DeepMessage = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Nested_InnerMessage_DeepMessage>): Nested_InnerMessage_DeepMessage {
+  fromPartial<I extends Exact<DeepPartial<Nested_InnerMessage_DeepMessage>, I>>(
+    object: I
+  ): Nested_InnerMessage_DeepMessage {
     const message = { ...baseNested_InnerMessage_DeepMessage } as Nested_InnerMessage_DeepMessage;
     message.name = object.name ?? '';
     return message;
@@ -681,7 +683,7 @@ export const OneOfMessage = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<OneOfMessage>): OneOfMessage {
+  fromPartial<I extends Exact<DeepPartial<OneOfMessage>, I>>(object: I): OneOfMessage {
     const message = { ...baseOneOfMessage } as OneOfMessage;
     message.first = object.first ?? undefined;
     message.last = object.last ?? undefined;
@@ -771,13 +773,13 @@ export const SimpleWithWrappers = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<SimpleWithWrappers>): SimpleWithWrappers {
+  fromPartial<I extends Exact<DeepPartial<SimpleWithWrappers>, I>>(object: I): SimpleWithWrappers {
     const message = { ...baseSimpleWithWrappers } as SimpleWithWrappers;
     message.name = object.name ?? undefined;
     message.age = object.age ?? undefined;
     message.enabled = object.enabled ?? undefined;
-    message.coins = (object.coins ?? []).map((e) => e);
-    message.snacks = (object.snacks ?? []).map((e) => e);
+    message.coins = object.coins?.map((e) => e) || [];
+    message.snacks = object.snacks?.map((e) => e) || [];
     return message;
   },
 };
@@ -822,7 +824,7 @@ export const Entity = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Entity>): Entity {
+  fromPartial<I extends Exact<DeepPartial<Entity>, I>>(object: I): Entity {
     const message = { ...baseEntity } as Entity;
     message.id = object.id ?? 0;
     return message;
@@ -930,7 +932,7 @@ export const SimpleWithMap = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<SimpleWithMap>): SimpleWithMap {
+  fromPartial<I extends Exact<DeepPartial<SimpleWithMap>, I>>(object: I): SimpleWithMap {
     const message = { ...baseSimpleWithMap } as SimpleWithMap;
     message.entitiesById = Object.entries(object.entitiesById ?? {}).reduce<{ [key: number]: Entity }>(
       (acc, [key, value]) => {
@@ -1011,7 +1013,9 @@ export const SimpleWithMap_EntitiesByIdEntry = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<SimpleWithMap_EntitiesByIdEntry>): SimpleWithMap_EntitiesByIdEntry {
+  fromPartial<I extends Exact<DeepPartial<SimpleWithMap_EntitiesByIdEntry>, I>>(
+    object: I
+  ): SimpleWithMap_EntitiesByIdEntry {
     const message = { ...baseSimpleWithMap_EntitiesByIdEntry } as SimpleWithMap_EntitiesByIdEntry;
     message.key = object.key ?? 0;
     message.value = object.value !== undefined && object.value !== null ? Entity.fromPartial(object.value) : undefined;
@@ -1067,7 +1071,9 @@ export const SimpleWithMap_NameLookupEntry = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<SimpleWithMap_NameLookupEntry>): SimpleWithMap_NameLookupEntry {
+  fromPartial<I extends Exact<DeepPartial<SimpleWithMap_NameLookupEntry>, I>>(
+    object: I
+  ): SimpleWithMap_NameLookupEntry {
     const message = { ...baseSimpleWithMap_NameLookupEntry } as SimpleWithMap_NameLookupEntry;
     message.key = object.key ?? '';
     message.value = object.value ?? '';
@@ -1123,7 +1129,7 @@ export const SimpleWithMap_IntLookupEntry = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<SimpleWithMap_IntLookupEntry>): SimpleWithMap_IntLookupEntry {
+  fromPartial<I extends Exact<DeepPartial<SimpleWithMap_IntLookupEntry>, I>>(object: I): SimpleWithMap_IntLookupEntry {
     const message = { ...baseSimpleWithMap_IntLookupEntry } as SimpleWithMap_IntLookupEntry;
     message.key = object.key ?? 0;
     message.value = object.value ?? 0;
@@ -1186,7 +1192,7 @@ export const SimpleWithSnakeCaseMap = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<SimpleWithSnakeCaseMap>): SimpleWithSnakeCaseMap {
+  fromPartial<I extends Exact<DeepPartial<SimpleWithSnakeCaseMap>, I>>(object: I): SimpleWithSnakeCaseMap {
     const message = { ...baseSimpleWithSnakeCaseMap } as SimpleWithSnakeCaseMap;
     message.entitiesById = Object.entries(object.entitiesById ?? {}).reduce<{ [key: number]: Entity }>(
       (acc, [key, value]) => {
@@ -1249,7 +1255,9 @@ export const SimpleWithSnakeCaseMap_EntitiesByIdEntry = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<SimpleWithSnakeCaseMap_EntitiesByIdEntry>): SimpleWithSnakeCaseMap_EntitiesByIdEntry {
+  fromPartial<I extends Exact<DeepPartial<SimpleWithSnakeCaseMap_EntitiesByIdEntry>, I>>(
+    object: I
+  ): SimpleWithSnakeCaseMap_EntitiesByIdEntry {
     const message = { ...baseSimpleWithSnakeCaseMap_EntitiesByIdEntry } as SimpleWithSnakeCaseMap_EntitiesByIdEntry;
     message.key = object.key ?? 0;
     message.value = object.value !== undefined && object.value !== null ? Entity.fromPartial(object.value) : undefined;
@@ -1297,7 +1305,7 @@ export const PingRequest = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<PingRequest>): PingRequest {
+  fromPartial<I extends Exact<DeepPartial<PingRequest>, I>>(object: I): PingRequest {
     const message = { ...basePingRequest } as PingRequest;
     message.input = object.input ?? '';
     return message;
@@ -1344,7 +1352,7 @@ export const PingResponse = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<PingResponse>): PingResponse {
+  fromPartial<I extends Exact<DeepPartial<PingResponse>, I>>(object: I): PingResponse {
     const message = { ...basePingResponse } as PingResponse;
     message.output = object.output ?? '';
     return message;
@@ -1492,7 +1500,7 @@ export const Numbers = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Numbers>): Numbers {
+  fromPartial<I extends Exact<DeepPartial<Numbers>, I>>(object: I): Numbers {
     const message = { ...baseNumbers } as Numbers;
     message.double = object.double ?? 0;
     message.float = object.float ?? 0;
@@ -1543,6 +1551,7 @@ var globalThis: any = (() => {
 })();
 
 type Builtin = Date | Function | Uint8Array | string | number | boolean | undefined;
+
 export type DeepPartial<T> = T extends Builtin
   ? T
   : T extends Array<infer U>
@@ -1553,6 +1562,11 @@ export type DeepPartial<T> = T extends Builtin
   ? { [K in keyof T]?: DeepPartial<T[K]> }
   : Partial<T>;
 
+type KeysOfUnion<T> = T extends T ? keyof T : never;
+export type Exact<P, I extends P> = P extends Builtin
+  ? P
+  : P & { [K in keyof P]: Exact<P[K], I[K]> } & Record<Exclude<keyof I, KeysOfUnion<P>>, never>;
+
 function toTimestamp(date: Date): Timestamp {
   const seconds = date.getTime() / 1_000;
   const nanos = (date.getTime() % 1_000) * 1_000_000;
diff --git a/integration/simple/google/protobuf/timestamp.ts b/integration/simple/google/protobuf/timestamp.ts
index e4600a73e..0670c17fd 100644
--- a/integration/simple/google/protobuf/timestamp.ts
+++ b/integration/simple/google/protobuf/timestamp.ts
@@ -161,7 +161,7 @@ export const Timestamp = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Timestamp>): Timestamp {
+  fromPartial<I extends Exact<DeepPartial<Timestamp>, I>>(object: I): Timestamp {
     const message = { ...baseTimestamp } as Timestamp;
     message.seconds = object.seconds ?? 0;
     message.nanos = object.nanos ?? 0;
@@ -181,6 +181,7 @@ var globalThis: any = (() => {
 })();
 
 type Builtin = Date | Function | Uint8Array | string | number | boolean | undefined;
+
 export type DeepPartial<T> = T extends Builtin
   ? T
   : T extends Array<infer U>
@@ -191,6 +192,11 @@ export type DeepPartial<T> = T extends Builtin
   ? { [K in keyof T]?: DeepPartial<T[K]> }
   : Partial<T>;
 
+type KeysOfUnion<T> = T extends T ? keyof T : never;
+export type Exact<P, I extends P> = P extends Builtin
+  ? P
+  : P & { [K in keyof P]: Exact<P[K], I[K]> } & Record<Exclude<keyof I, KeysOfUnion<P>>, never>;
+
 function longToNumber(long: Long): number {
   if (long.gt(Number.MAX_SAFE_INTEGER)) {
     throw new globalThis.Error('Value is larger than Number.MAX_SAFE_INTEGER');
diff --git a/integration/simple/google/protobuf/wrappers.ts b/integration/simple/google/protobuf/wrappers.ts
index 216285744..35b159990 100644
--- a/integration/simple/google/protobuf/wrappers.ts
+++ b/integration/simple/google/protobuf/wrappers.ts
@@ -134,7 +134,7 @@ export const DoubleValue = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<DoubleValue>): DoubleValue {
+  fromPartial<I extends Exact<DeepPartial<DoubleValue>, I>>(object: I): DoubleValue {
     const message = { ...baseDoubleValue } as DoubleValue;
     message.value = object.value ?? 0;
     return message;
@@ -181,7 +181,7 @@ export const FloatValue = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<FloatValue>): FloatValue {
+  fromPartial<I extends Exact<DeepPartial<FloatValue>, I>>(object: I): FloatValue {
     const message = { ...baseFloatValue } as FloatValue;
     message.value = object.value ?? 0;
     return message;
@@ -228,7 +228,7 @@ export const Int64Value = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Int64Value>): Int64Value {
+  fromPartial<I extends Exact<DeepPartial<Int64Value>, I>>(object: I): Int64Value {
     const message = { ...baseInt64Value } as Int64Value;
     message.value = object.value ?? 0;
     return message;
@@ -275,7 +275,7 @@ export const UInt64Value = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<UInt64Value>): UInt64Value {
+  fromPartial<I extends Exact<DeepPartial<UInt64Value>, I>>(object: I): UInt64Value {
     const message = { ...baseUInt64Value } as UInt64Value;
     message.value = object.value ?? 0;
     return message;
@@ -322,7 +322,7 @@ export const Int32Value = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Int32Value>): Int32Value {
+  fromPartial<I extends Exact<DeepPartial<Int32Value>, I>>(object: I): Int32Value {
     const message = { ...baseInt32Value } as Int32Value;
     message.value = object.value ?? 0;
     return message;
@@ -369,7 +369,7 @@ export const UInt32Value = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<UInt32Value>): UInt32Value {
+  fromPartial<I extends Exact<DeepPartial<UInt32Value>, I>>(object: I): UInt32Value {
     const message = { ...baseUInt32Value } as UInt32Value;
     message.value = object.value ?? 0;
     return message;
@@ -416,7 +416,7 @@ export const BoolValue = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<BoolValue>): BoolValue {
+  fromPartial<I extends Exact<DeepPartial<BoolValue>, I>>(object: I): BoolValue {
     const message = { ...baseBoolValue } as BoolValue;
     message.value = object.value ?? false;
     return message;
@@ -463,7 +463,7 @@ export const StringValue = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<StringValue>): StringValue {
+  fromPartial<I extends Exact<DeepPartial<StringValue>, I>>(object: I): StringValue {
     const message = { ...baseStringValue } as StringValue;
     message.value = object.value ?? '';
     return message;
@@ -513,7 +513,7 @@ export const BytesValue = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<BytesValue>): BytesValue {
+  fromPartial<I extends Exact<DeepPartial<BytesValue>, I>>(object: I): BytesValue {
     const message = { ...baseBytesValue } as BytesValue;
     message.value = object.value ?? new Uint8Array();
     return message;
@@ -553,6 +553,7 @@ function base64FromBytes(arr: Uint8Array): string {
 }
 
 type Builtin = Date | Function | Uint8Array | string | number | boolean | undefined;
+
 export type DeepPartial<T> = T extends Builtin
   ? T
   : T extends Array<infer U>
@@ -563,6 +564,11 @@ export type DeepPartial<T> = T extends Builtin
   ? { [K in keyof T]?: DeepPartial<T[K]> }
   : Partial<T>;
 
+type KeysOfUnion<T> = T extends T ? keyof T : never;
+export type Exact<P, I extends P> = P extends Builtin
+  ? P
+  : P & { [K in keyof P]: Exact<P[K], I[K]> } & Record<Exclude<keyof I, KeysOfUnion<P>>, never>;
+
 function longToNumber(long: Long): number {
   if (long.gt(Number.MAX_SAFE_INTEGER)) {
     throw new globalThis.Error('Value is larger than Number.MAX_SAFE_INTEGER');
diff --git a/integration/simple/google/type/date.ts b/integration/simple/google/type/date.ts
index 88b392a00..d29072413 100644
--- a/integration/simple/google/type/date.ts
+++ b/integration/simple/google/type/date.ts
@@ -91,7 +91,7 @@ export const DateMessage = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<DateMessage>): DateMessage {
+  fromPartial<I extends Exact<DeepPartial<DateMessage>, I>>(object: I): DateMessage {
     const message = { ...baseDateMessage } as DateMessage;
     message.year = object.year ?? 0;
     message.month = object.month ?? 0;
@@ -101,6 +101,7 @@ export const DateMessage = {
 };
 
 type Builtin = Date | Function | Uint8Array | string | number | boolean | undefined;
+
 export type DeepPartial<T> = T extends Builtin
   ? T
   : T extends Array<infer U>
@@ -111,6 +112,11 @@ export type DeepPartial<T> = T extends Builtin
   ? { [K in keyof T]?: DeepPartial<T[K]> }
   : Partial<T>;
 
+type KeysOfUnion<T> = T extends T ? keyof T : never;
+export type Exact<P, I extends P> = P extends Builtin
+  ? P
+  : P & { [K in keyof P]: Exact<P[K], I[K]> } & Record<Exclude<keyof I, KeysOfUnion<P>>, never>;
+
 // If you get a compile-error about 'Constructor<Long> and ... have no overlap',
 // add '--ts_proto_opt=esModuleInterop=true' as a flag when calling 'protoc'.
 if (util.Long !== Long) {
diff --git a/integration/simple/import_dir/thing.ts b/integration/simple/import_dir/thing.ts
index 276e91e85..6a1771dcc 100644
--- a/integration/simple/import_dir/thing.ts
+++ b/integration/simple/import_dir/thing.ts
@@ -50,7 +50,7 @@ export const ImportedThing = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<ImportedThing>): ImportedThing {
+  fromPartial<I extends Exact<DeepPartial<ImportedThing>, I>>(object: I): ImportedThing {
     const message = { ...baseImportedThing } as ImportedThing;
     message.createdAt = object.createdAt ?? undefined;
     return message;
@@ -58,6 +58,7 @@ export const ImportedThing = {
 };
 
 type Builtin = Date | Function | Uint8Array | string | number | boolean | undefined;
+
 export type DeepPartial<T> = T extends Builtin
   ? T
   : T extends Array<infer U>
@@ -68,6 +69,11 @@ export type DeepPartial<T> = T extends Builtin
   ? { [K in keyof T]?: DeepPartial<T[K]> }
   : Partial<T>;
 
+type KeysOfUnion<T> = T extends T ? keyof T : never;
+export type Exact<P, I extends P> = P extends Builtin
+  ? P
+  : P & { [K in keyof P]: Exact<P[K], I[K]> } & Record<Exclude<keyof I, KeysOfUnion<P>>, never>;
+
 function toTimestamp(date: Date): Timestamp {
   const seconds = date.getTime() / 1_000;
   const nanos = (date.getTime() % 1_000) * 1_000_000;
diff --git a/integration/simple/simple-test.ts b/integration/simple/simple-test.ts
index f87be3048..e57c21cad 100644
--- a/integration/simple/simple-test.ts
+++ b/integration/simple/simple-test.ts
@@ -320,6 +320,13 @@ describe('simple', () => {
     `);
   });
 
+  it('has fromPartial uses exact types', () => {
+    const s1 = Simple.fromPartial({
+      // @ts-expect-error
+      grandChildren: ['a', 'b'].map((name) => ({ name, typ: null })),
+    });
+  });
+
   it('can fromPartial on maps with falsey values', () => {
     const s1 = SimpleWithMap.fromPartial({
       intLookup: { 1: 2, 2: 0 },
diff --git a/integration/simple/simple.ts b/integration/simple/simple.ts
index 93d273821..19369e188 100644
--- a/integration/simple/simple.ts
+++ b/integration/simple/simple.ts
@@ -475,20 +475,20 @@ export const Simple = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Simple>): Simple {
+  fromPartial<I extends Exact<DeepPartial<Simple>, I>>(object: I): Simple {
     const message = { ...baseSimple } as Simple;
     message.name = object.name ?? '';
     message.age = object.age ?? 0;
     message.createdAt = object.createdAt ?? undefined;
     message.child = object.child !== undefined && object.child !== null ? Child.fromPartial(object.child) : undefined;
     message.state = object.state ?? 0;
-    message.grandChildren = (object.grandChildren ?? []).map((e) => Child.fromPartial(e));
-    message.coins = (object.coins ?? []).map((e) => e);
-    message.snacks = (object.snacks ?? []).map((e) => e);
-    message.oldStates = (object.oldStates ?? []).map((e) => e);
+    message.grandChildren = object.grandChildren?.map((e) => Child.fromPartial(e)) || [];
+    message.coins = object.coins?.map((e) => e) || [];
+    message.snacks = object.snacks?.map((e) => e) || [];
+    message.oldStates = object.oldStates?.map((e) => e) || [];
     message.thing =
       object.thing !== undefined && object.thing !== null ? ImportedThing.fromPartial(object.thing) : undefined;
-    message.blobs = (object.blobs ?? []).map((e) => e);
+    message.blobs = object.blobs?.map((e) => e) || [];
     message.birthday =
       object.birthday !== undefined && object.birthday !== null ? DateMessage.fromPartial(object.birthday) : undefined;
     message.blob = object.blob ?? new Uint8Array();
@@ -544,7 +544,7 @@ export const Child = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Child>): Child {
+  fromPartial<I extends Exact<DeepPartial<Child>, I>>(object: I): Child {
     const message = { ...baseChild } as Child;
     message.name = object.name ?? '';
     message.type = object.type ?? 0;
@@ -612,7 +612,7 @@ export const Nested = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Nested>): Nested {
+  fromPartial<I extends Exact<DeepPartial<Nested>, I>>(object: I): Nested {
     const message = { ...baseNested } as Nested;
     message.name = object.name ?? '';
     message.message =
@@ -676,7 +676,7 @@ export const Nested_InnerMessage = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Nested_InnerMessage>): Nested_InnerMessage {
+  fromPartial<I extends Exact<DeepPartial<Nested_InnerMessage>, I>>(object: I): Nested_InnerMessage {
     const message = { ...baseNested_InnerMessage } as Nested_InnerMessage;
     message.name = object.name ?? '';
     message.deep =
@@ -727,7 +727,9 @@ export const Nested_InnerMessage_DeepMessage = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Nested_InnerMessage_DeepMessage>): Nested_InnerMessage_DeepMessage {
+  fromPartial<I extends Exact<DeepPartial<Nested_InnerMessage_DeepMessage>, I>>(
+    object: I
+  ): Nested_InnerMessage_DeepMessage {
     const message = { ...baseNested_InnerMessage_DeepMessage } as Nested_InnerMessage_DeepMessage;
     message.name = object.name ?? '';
     return message;
@@ -782,7 +784,7 @@ export const OneOfMessage = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<OneOfMessage>): OneOfMessage {
+  fromPartial<I extends Exact<DeepPartial<OneOfMessage>, I>>(object: I): OneOfMessage {
     const message = { ...baseOneOfMessage } as OneOfMessage;
     message.first = object.first ?? undefined;
     message.last = object.last ?? undefined;
@@ -880,13 +882,13 @@ export const SimpleWithWrappers = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<SimpleWithWrappers>): SimpleWithWrappers {
+  fromPartial<I extends Exact<DeepPartial<SimpleWithWrappers>, I>>(object: I): SimpleWithWrappers {
     const message = { ...baseSimpleWithWrappers } as SimpleWithWrappers;
     message.name = object.name ?? undefined;
     message.age = object.age ?? undefined;
     message.enabled = object.enabled ?? undefined;
-    message.coins = (object.coins ?? []).map((e) => e);
-    message.snacks = (object.snacks ?? []).map((e) => e);
+    message.coins = object.coins?.map((e) => e) || [];
+    message.snacks = object.snacks?.map((e) => e) || [];
     message.id = object.id ?? undefined;
     return message;
   },
@@ -932,7 +934,7 @@ export const Entity = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Entity>): Entity {
+  fromPartial<I extends Exact<DeepPartial<Entity>, I>>(object: I): Entity {
     const message = { ...baseEntity } as Entity;
     message.id = object.id ?? 0;
     return message;
@@ -1133,7 +1135,7 @@ export const SimpleWithMap = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<SimpleWithMap>): SimpleWithMap {
+  fromPartial<I extends Exact<DeepPartial<SimpleWithMap>, I>>(object: I): SimpleWithMap {
     const message = { ...baseSimpleWithMap } as SimpleWithMap;
     message.entitiesById = Object.entries(object.entitiesById ?? {}).reduce<{ [key: number]: Entity }>(
       (acc, [key, value]) => {
@@ -1249,7 +1251,9 @@ export const SimpleWithMap_EntitiesByIdEntry = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<SimpleWithMap_EntitiesByIdEntry>): SimpleWithMap_EntitiesByIdEntry {
+  fromPartial<I extends Exact<DeepPartial<SimpleWithMap_EntitiesByIdEntry>, I>>(
+    object: I
+  ): SimpleWithMap_EntitiesByIdEntry {
     const message = { ...baseSimpleWithMap_EntitiesByIdEntry } as SimpleWithMap_EntitiesByIdEntry;
     message.key = object.key ?? 0;
     message.value = object.value !== undefined && object.value !== null ? Entity.fromPartial(object.value) : undefined;
@@ -1305,7 +1309,9 @@ export const SimpleWithMap_NameLookupEntry = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<SimpleWithMap_NameLookupEntry>): SimpleWithMap_NameLookupEntry {
+  fromPartial<I extends Exact<DeepPartial<SimpleWithMap_NameLookupEntry>, I>>(
+    object: I
+  ): SimpleWithMap_NameLookupEntry {
     const message = { ...baseSimpleWithMap_NameLookupEntry } as SimpleWithMap_NameLookupEntry;
     message.key = object.key ?? '';
     message.value = object.value ?? '';
@@ -1361,7 +1367,7 @@ export const SimpleWithMap_IntLookupEntry = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<SimpleWithMap_IntLookupEntry>): SimpleWithMap_IntLookupEntry {
+  fromPartial<I extends Exact<DeepPartial<SimpleWithMap_IntLookupEntry>, I>>(object: I): SimpleWithMap_IntLookupEntry {
     const message = { ...baseSimpleWithMap_IntLookupEntry } as SimpleWithMap_IntLookupEntry;
     message.key = object.key ?? 0;
     message.value = object.value ?? 0;
@@ -1417,7 +1423,9 @@ export const SimpleWithMap_MapOfTimestampsEntry = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<SimpleWithMap_MapOfTimestampsEntry>): SimpleWithMap_MapOfTimestampsEntry {
+  fromPartial<I extends Exact<DeepPartial<SimpleWithMap_MapOfTimestampsEntry>, I>>(
+    object: I
+  ): SimpleWithMap_MapOfTimestampsEntry {
     const message = { ...baseSimpleWithMap_MapOfTimestampsEntry } as SimpleWithMap_MapOfTimestampsEntry;
     message.key = object.key ?? '';
     message.value = object.value ?? undefined;
@@ -1476,7 +1484,9 @@ export const SimpleWithMap_MapOfBytesEntry = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<SimpleWithMap_MapOfBytesEntry>): SimpleWithMap_MapOfBytesEntry {
+  fromPartial<I extends Exact<DeepPartial<SimpleWithMap_MapOfBytesEntry>, I>>(
+    object: I
+  ): SimpleWithMap_MapOfBytesEntry {
     const message = { ...baseSimpleWithMap_MapOfBytesEntry } as SimpleWithMap_MapOfBytesEntry;
     message.key = object.key ?? '';
     message.value = object.value ?? new Uint8Array();
@@ -1532,7 +1542,9 @@ export const SimpleWithMap_MapOfStringValuesEntry = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<SimpleWithMap_MapOfStringValuesEntry>): SimpleWithMap_MapOfStringValuesEntry {
+  fromPartial<I extends Exact<DeepPartial<SimpleWithMap_MapOfStringValuesEntry>, I>>(
+    object: I
+  ): SimpleWithMap_MapOfStringValuesEntry {
     const message = { ...baseSimpleWithMap_MapOfStringValuesEntry } as SimpleWithMap_MapOfStringValuesEntry;
     message.key = object.key ?? '';
     message.value = object.value ?? undefined;
@@ -1588,7 +1600,9 @@ export const SimpleWithMap_LongLookupEntry = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<SimpleWithMap_LongLookupEntry>): SimpleWithMap_LongLookupEntry {
+  fromPartial<I extends Exact<DeepPartial<SimpleWithMap_LongLookupEntry>, I>>(
+    object: I
+  ): SimpleWithMap_LongLookupEntry {
     const message = { ...baseSimpleWithMap_LongLookupEntry } as SimpleWithMap_LongLookupEntry;
     message.key = object.key ?? 0;
     message.value = object.value ?? 0;
@@ -1651,7 +1665,7 @@ export const SimpleWithSnakeCaseMap = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<SimpleWithSnakeCaseMap>): SimpleWithSnakeCaseMap {
+  fromPartial<I extends Exact<DeepPartial<SimpleWithSnakeCaseMap>, I>>(object: I): SimpleWithSnakeCaseMap {
     const message = { ...baseSimpleWithSnakeCaseMap } as SimpleWithSnakeCaseMap;
     message.entitiesById = Object.entries(object.entitiesById ?? {}).reduce<{ [key: number]: Entity }>(
       (acc, [key, value]) => {
@@ -1714,7 +1728,9 @@ export const SimpleWithSnakeCaseMap_EntitiesByIdEntry = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<SimpleWithSnakeCaseMap_EntitiesByIdEntry>): SimpleWithSnakeCaseMap_EntitiesByIdEntry {
+  fromPartial<I extends Exact<DeepPartial<SimpleWithSnakeCaseMap_EntitiesByIdEntry>, I>>(
+    object: I
+  ): SimpleWithSnakeCaseMap_EntitiesByIdEntry {
     const message = { ...baseSimpleWithSnakeCaseMap_EntitiesByIdEntry } as SimpleWithSnakeCaseMap_EntitiesByIdEntry;
     message.key = object.key ?? 0;
     message.value = object.value !== undefined && object.value !== null ? Entity.fromPartial(object.value) : undefined;
@@ -1777,7 +1793,7 @@ export const SimpleWithMapOfEnums = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<SimpleWithMapOfEnums>): SimpleWithMapOfEnums {
+  fromPartial<I extends Exact<DeepPartial<SimpleWithMapOfEnums>, I>>(object: I): SimpleWithMapOfEnums {
     const message = { ...baseSimpleWithMapOfEnums } as SimpleWithMapOfEnums;
     message.enumsById = Object.entries(object.enumsById ?? {}).reduce<{ [key: number]: StateEnum }>(
       (acc, [key, value]) => {
@@ -1840,7 +1856,9 @@ export const SimpleWithMapOfEnums_EnumsByIdEntry = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<SimpleWithMapOfEnums_EnumsByIdEntry>): SimpleWithMapOfEnums_EnumsByIdEntry {
+  fromPartial<I extends Exact<DeepPartial<SimpleWithMapOfEnums_EnumsByIdEntry>, I>>(
+    object: I
+  ): SimpleWithMapOfEnums_EnumsByIdEntry {
     const message = { ...baseSimpleWithMapOfEnums_EnumsByIdEntry } as SimpleWithMapOfEnums_EnumsByIdEntry;
     message.key = object.key ?? 0;
     message.value = object.value ?? 0;
@@ -1888,7 +1906,7 @@ export const PingRequest = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<PingRequest>): PingRequest {
+  fromPartial<I extends Exact<DeepPartial<PingRequest>, I>>(object: I): PingRequest {
     const message = { ...basePingRequest } as PingRequest;
     message.input = object.input ?? '';
     return message;
@@ -1935,7 +1953,7 @@ export const PingResponse = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<PingResponse>): PingResponse {
+  fromPartial<I extends Exact<DeepPartial<PingResponse>, I>>(object: I): PingResponse {
     const message = { ...basePingResponse } as PingResponse;
     message.output = object.output ?? '';
     return message;
@@ -2083,7 +2101,7 @@ export const Numbers = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Numbers>): Numbers {
+  fromPartial<I extends Exact<DeepPartial<Numbers>, I>>(object: I): Numbers {
     const message = { ...baseNumbers } as Numbers;
     message.double = object.double ?? 0;
     message.float = object.float ?? 0;
@@ -2194,7 +2212,7 @@ export const SimpleButOptional = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<SimpleButOptional>): SimpleButOptional {
+  fromPartial<I extends Exact<DeepPartial<SimpleButOptional>, I>>(object: I): SimpleButOptional {
     const message = { ...baseSimpleButOptional } as SimpleButOptional;
     message.name = object.name ?? undefined;
     message.age = object.age ?? undefined;
@@ -2241,7 +2259,7 @@ export const Empty = {
     return obj;
   },
 
-  fromPartial(_: DeepPartial<Empty>): Empty {
+  fromPartial<I extends Exact<DeepPartial<Empty>, I>>(_: I): Empty {
     const message = { ...baseEmpty } as Empty;
     return message;
   },
@@ -2301,6 +2319,7 @@ function base64FromBytes(arr: Uint8Array): string {
 }
 
 type Builtin = Date | Function | Uint8Array | string | number | boolean | undefined;
+
 export type DeepPartial<T> = T extends Builtin
   ? T
   : T extends Array<infer U>
@@ -2311,6 +2330,11 @@ export type DeepPartial<T> = T extends Builtin
   ? { [K in keyof T]?: DeepPartial<T[K]> }
   : Partial<T>;
 
+type KeysOfUnion<T> = T extends T ? keyof T : never;
+export type Exact<P, I extends P> = P extends Builtin
+  ? P
+  : P & { [K in keyof P]: Exact<P[K], I[K]> } & Record<Exclude<keyof I, KeysOfUnion<P>>, never>;
+
 function toTimestamp(date: Date): Timestamp {
   const seconds = date.getTime() / 1_000;
   const nanos = (date.getTime() % 1_000) * 1_000_000;
diff --git a/integration/struct/google/protobuf/struct.ts b/integration/struct/google/protobuf/struct.ts
index a2b7d6f54..28fe05424 100644
--- a/integration/struct/google/protobuf/struct.ts
+++ b/integration/struct/google/protobuf/struct.ts
@@ -147,7 +147,7 @@ export const Struct = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Struct>): Struct {
+  fromPartial<I extends Exact<DeepPartial<Struct>, I>>(object: I): Struct {
     const message = { ...baseStruct } as Struct;
     message.fields = Object.entries(object.fields ?? {}).reduce<{ [key: string]: any | undefined }>(
       (acc, [key, value]) => {
@@ -228,7 +228,7 @@ export const Struct_FieldsEntry = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Struct_FieldsEntry>): Struct_FieldsEntry {
+  fromPartial<I extends Exact<DeepPartial<Struct_FieldsEntry>, I>>(object: I): Struct_FieldsEntry {
     const message = { ...baseStruct_FieldsEntry } as Struct_FieldsEntry;
     message.key = object.key ?? '';
     message.value = object.value ?? undefined;
@@ -321,7 +321,7 @@ export const Value = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Value>): Value {
+  fromPartial<I extends Exact<DeepPartial<Value>, I>>(object: I): Value {
     const message = { ...baseValue } as Value;
     message.nullValue = object.nullValue ?? undefined;
     message.numberValue = object.numberValue ?? undefined;
@@ -414,9 +414,9 @@ export const ListValue = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<ListValue>): ListValue {
+  fromPartial<I extends Exact<DeepPartial<ListValue>, I>>(object: I): ListValue {
     const message = { ...baseListValue } as ListValue;
-    message.values = (object.values ?? []).map((e) => e);
+    message.values = object.values?.map((e) => e) || [];
     return message;
   },
 
@@ -430,6 +430,7 @@ export const ListValue = {
 };
 
 type Builtin = Date | Function | Uint8Array | string | number | boolean | undefined;
+
 export type DeepPartial<T> = T extends Builtin
   ? T
   : T extends Array<infer U>
@@ -440,6 +441,11 @@ export type DeepPartial<T> = T extends Builtin
   ? { [K in keyof T]?: DeepPartial<T[K]> }
   : Partial<T>;
 
+type KeysOfUnion<T> = T extends T ? keyof T : never;
+export type Exact<P, I extends P> = P extends Builtin
+  ? P
+  : P & { [K in keyof P]: Exact<P[K], I[K]> } & Record<Exclude<keyof I, KeysOfUnion<P>>, never>;
+
 // If you get a compile-error about 'Constructor<Long> and ... have no overlap',
 // add '--ts_proto_opt=esModuleInterop=true' as a flag when calling 'protoc'.
 if (util.Long !== Long) {
diff --git a/integration/struct/struct.ts b/integration/struct/struct.ts
index b2bf7dbc4..7ed1f3ed5 100644
--- a/integration/struct/struct.ts
+++ b/integration/struct/struct.ts
@@ -49,7 +49,7 @@ export const StructMessage = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<StructMessage>): StructMessage {
+  fromPartial<I extends Exact<DeepPartial<StructMessage>, I>>(object: I): StructMessage {
     const message = { ...baseStructMessage } as StructMessage;
     message.value = object.value ?? undefined;
     return message;
@@ -57,6 +57,7 @@ export const StructMessage = {
 };
 
 type Builtin = Date | Function | Uint8Array | string | number | boolean | undefined;
+
 export type DeepPartial<T> = T extends Builtin
   ? T
   : T extends Array<infer U>
@@ -67,6 +68,11 @@ export type DeepPartial<T> = T extends Builtin
   ? { [K in keyof T]?: DeepPartial<T[K]> }
   : Partial<T>;
 
+type KeysOfUnion<T> = T extends T ? keyof T : never;
+export type Exact<P, I extends P> = P extends Builtin
+  ? P
+  : P & { [K in keyof P]: Exact<P[K], I[K]> } & Record<Exclude<keyof I, KeysOfUnion<P>>, never>;
+
 // If you get a compile-error about 'Constructor<Long> and ... have no overlap',
 // add '--ts_proto_opt=esModuleInterop=true' as a flag when calling 'protoc'.
 if (util.Long !== Long) {
diff --git a/integration/type-registry/bar/bar.ts b/integration/type-registry/bar/bar.ts
index 5df3681c5..60cafe6fa 100644
--- a/integration/type-registry/bar/bar.ts
+++ b/integration/type-registry/bar/bar.ts
@@ -53,7 +53,7 @@ export const Bar = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Bar>): Bar {
+  fromPartial<I extends Exact<DeepPartial<Bar>, I>>(object: I): Bar {
     const message = { ...baseBar } as Bar;
     message.foo = object.foo !== undefined && object.foo !== null ? Foo.fromPartial(object.foo) : undefined;
     return message;
@@ -63,6 +63,7 @@ export const Bar = {
 messageTypeRegistry.set(Bar.$type, Bar);
 
 type Builtin = Date | Function | Uint8Array | string | number | boolean | undefined;
+
 export type DeepPartial<T> = T extends Builtin
   ? T
   : T extends Array<infer U>
@@ -73,6 +74,11 @@ export type DeepPartial<T> = T extends Builtin
   ? { [K in Exclude<keyof T, '$type'>]?: DeepPartial<T[K]> }
   : Partial<T>;
 
+type KeysOfUnion<T> = T extends T ? keyof T : never;
+export type Exact<P, I extends P> = P extends Builtin
+  ? P
+  : P & { [K in keyof P]: Exact<P[K], I[K]> } & Record<Exclude<keyof I, KeysOfUnion<P> | '$type'>, never>;
+
 // If you get a compile-error about 'Constructor<Long> and ... have no overlap',
 // add '--ts_proto_opt=esModuleInterop=true' as a flag when calling 'protoc'.
 if (util.Long !== Long) {
diff --git a/integration/type-registry/foo.ts b/integration/type-registry/foo.ts
index 1f7edbc2e..2f9d88546 100644
--- a/integration/type-registry/foo.ts
+++ b/integration/type-registry/foo.ts
@@ -59,7 +59,7 @@ export const Foo = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Foo>): Foo {
+  fromPartial<I extends Exact<DeepPartial<Foo>, I>>(object: I): Foo {
     const message = { ...baseFoo } as Foo;
     message.timestamp = object.timestamp ?? undefined;
     return message;
@@ -111,7 +111,7 @@ export const Foo2 = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Foo2>): Foo2 {
+  fromPartial<I extends Exact<DeepPartial<Foo2>, I>>(object: I): Foo2 {
     const message = { ...baseFoo2 } as Foo2;
     message.timestamp = object.timestamp ?? undefined;
     return message;
@@ -121,6 +121,7 @@ export const Foo2 = {
 messageTypeRegistry.set(Foo2.$type, Foo2);
 
 type Builtin = Date | Function | Uint8Array | string | number | boolean | undefined;
+
 export type DeepPartial<T> = T extends Builtin
   ? T
   : T extends Array<infer U>
@@ -131,6 +132,11 @@ export type DeepPartial<T> = T extends Builtin
   ? { [K in Exclude<keyof T, '$type'>]?: DeepPartial<T[K]> }
   : Partial<T>;
 
+type KeysOfUnion<T> = T extends T ? keyof T : never;
+export type Exact<P, I extends P> = P extends Builtin
+  ? P
+  : P & { [K in keyof P]: Exact<P[K], I[K]> } & Record<Exclude<keyof I, KeysOfUnion<P> | '$type'>, never>;
+
 function toTimestamp(date: Date): Timestamp {
   const seconds = date.getTime() / 1_000;
   const nanos = (date.getTime() % 1_000) * 1_000_000;
diff --git a/integration/type-registry/google/protobuf/timestamp.ts b/integration/type-registry/google/protobuf/timestamp.ts
index 2f723335c..17a482643 100644
--- a/integration/type-registry/google/protobuf/timestamp.ts
+++ b/integration/type-registry/google/protobuf/timestamp.ts
@@ -165,7 +165,7 @@ export const Timestamp = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Timestamp>): Timestamp {
+  fromPartial<I extends Exact<DeepPartial<Timestamp>, I>>(object: I): Timestamp {
     const message = { ...baseTimestamp } as Timestamp;
     message.seconds = object.seconds ?? 0;
     message.nanos = object.nanos ?? 0;
@@ -187,6 +187,7 @@ var globalThis: any = (() => {
 })();
 
 type Builtin = Date | Function | Uint8Array | string | number | boolean | undefined;
+
 export type DeepPartial<T> = T extends Builtin
   ? T
   : T extends Array<infer U>
@@ -197,6 +198,11 @@ export type DeepPartial<T> = T extends Builtin
   ? { [K in Exclude<keyof T, '$type'>]?: DeepPartial<T[K]> }
   : Partial<T>;
 
+type KeysOfUnion<T> = T extends T ? keyof T : never;
+export type Exact<P, I extends P> = P extends Builtin
+  ? P
+  : P & { [K in keyof P]: Exact<P[K], I[K]> } & Record<Exclude<keyof I, KeysOfUnion<P> | '$type'>, never>;
+
 function longToNumber(long: Long): number {
   if (long.gt(Number.MAX_SAFE_INTEGER)) {
     throw new globalThis.Error('Value is larger than Number.MAX_SAFE_INTEGER');
diff --git a/integration/types-with-underscores/file.ts b/integration/types-with-underscores/file.ts
index 1b9aff8cb..d74b8eb1f 100644
--- a/integration/types-with-underscores/file.ts
+++ b/integration/types-with-underscores/file.ts
@@ -50,7 +50,7 @@ export const Baz = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Baz>): Baz {
+  fromPartial<I extends Exact<DeepPartial<Baz>, I>>(object: I): Baz {
     const message = { ...baseBaz } as Baz;
     message.foo = object.foo !== undefined && object.foo !== null ? FooBar.fromPartial(object.foo) : undefined;
     return message;
@@ -89,13 +89,14 @@ export const FooBar = {
     return obj;
   },
 
-  fromPartial(_: DeepPartial<FooBar>): FooBar {
+  fromPartial<I extends Exact<DeepPartial<FooBar>, I>>(_: I): FooBar {
     const message = { ...baseFooBar } as FooBar;
     return message;
   },
 };
 
 type Builtin = Date | Function | Uint8Array | string | number | boolean | undefined;
+
 export type DeepPartial<T> = T extends Builtin
   ? T
   : T extends Array<infer U>
@@ -106,6 +107,11 @@ export type DeepPartial<T> = T extends Builtin
   ? { [K in keyof T]?: DeepPartial<T[K]> }
   : Partial<T>;
 
+type KeysOfUnion<T> = T extends T ? keyof T : never;
+export type Exact<P, I extends P> = P extends Builtin
+  ? P
+  : P & { [K in keyof P]: Exact<P[K], I[K]> } & Record<Exclude<keyof I, KeysOfUnion<P>>, never>;
+
 // If you get a compile-error about 'Constructor<Long> and ... have no overlap',
 // add '--ts_proto_opt=esModuleInterop=true' as a flag when calling 'protoc'.
 if (util.Long !== Long) {
diff --git a/integration/use-date-false/google/protobuf/timestamp.ts b/integration/use-date-false/google/protobuf/timestamp.ts
index e4600a73e..0670c17fd 100644
--- a/integration/use-date-false/google/protobuf/timestamp.ts
+++ b/integration/use-date-false/google/protobuf/timestamp.ts
@@ -161,7 +161,7 @@ export const Timestamp = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Timestamp>): Timestamp {
+  fromPartial<I extends Exact<DeepPartial<Timestamp>, I>>(object: I): Timestamp {
     const message = { ...baseTimestamp } as Timestamp;
     message.seconds = object.seconds ?? 0;
     message.nanos = object.nanos ?? 0;
@@ -181,6 +181,7 @@ var globalThis: any = (() => {
 })();
 
 type Builtin = Date | Function | Uint8Array | string | number | boolean | undefined;
+
 export type DeepPartial<T> = T extends Builtin
   ? T
   : T extends Array<infer U>
@@ -191,6 +192,11 @@ export type DeepPartial<T> = T extends Builtin
   ? { [K in keyof T]?: DeepPartial<T[K]> }
   : Partial<T>;
 
+type KeysOfUnion<T> = T extends T ? keyof T : never;
+export type Exact<P, I extends P> = P extends Builtin
+  ? P
+  : P & { [K in keyof P]: Exact<P[K], I[K]> } & Record<Exclude<keyof I, KeysOfUnion<P>>, never>;
+
 function longToNumber(long: Long): number {
   if (long.gt(Number.MAX_SAFE_INTEGER)) {
     throw new globalThis.Error('Value is larger than Number.MAX_SAFE_INTEGER');
diff --git a/integration/use-date-false/metadata.ts b/integration/use-date-false/metadata.ts
index 1005399b6..e97264378 100644
--- a/integration/use-date-false/metadata.ts
+++ b/integration/use-date-false/metadata.ts
@@ -50,7 +50,7 @@ export const Metadata = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Metadata>): Metadata {
+  fromPartial<I extends Exact<DeepPartial<Metadata>, I>>(object: I): Metadata {
     const message = { ...baseMetadata } as Metadata;
     message.lastEdited =
       object.lastEdited !== undefined && object.lastEdited !== null
@@ -61,6 +61,7 @@ export const Metadata = {
 };
 
 type Builtin = Date | Function | Uint8Array | string | number | boolean | undefined;
+
 export type DeepPartial<T> = T extends Builtin
   ? T
   : T extends Array<infer U>
@@ -71,6 +72,11 @@ export type DeepPartial<T> = T extends Builtin
   ? { [K in keyof T]?: DeepPartial<T[K]> }
   : Partial<T>;
 
+type KeysOfUnion<T> = T extends T ? keyof T : never;
+export type Exact<P, I extends P> = P extends Builtin
+  ? P
+  : P & { [K in keyof P]: Exact<P[K], I[K]> } & Record<Exclude<keyof I, KeysOfUnion<P>>, never>;
+
 function toTimestamp(date: Date): Timestamp {
   const seconds = date.getTime() / 1_000;
   const nanos = (date.getTime() % 1_000) * 1_000_000;
diff --git a/integration/use-date-string/google/protobuf/timestamp.ts b/integration/use-date-string/google/protobuf/timestamp.ts
index e4600a73e..0670c17fd 100644
--- a/integration/use-date-string/google/protobuf/timestamp.ts
+++ b/integration/use-date-string/google/protobuf/timestamp.ts
@@ -161,7 +161,7 @@ export const Timestamp = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Timestamp>): Timestamp {
+  fromPartial<I extends Exact<DeepPartial<Timestamp>, I>>(object: I): Timestamp {
     const message = { ...baseTimestamp } as Timestamp;
     message.seconds = object.seconds ?? 0;
     message.nanos = object.nanos ?? 0;
@@ -181,6 +181,7 @@ var globalThis: any = (() => {
 })();
 
 type Builtin = Date | Function | Uint8Array | string | number | boolean | undefined;
+
 export type DeepPartial<T> = T extends Builtin
   ? T
   : T extends Array<infer U>
@@ -191,6 +192,11 @@ export type DeepPartial<T> = T extends Builtin
   ? { [K in keyof T]?: DeepPartial<T[K]> }
   : Partial<T>;
 
+type KeysOfUnion<T> = T extends T ? keyof T : never;
+export type Exact<P, I extends P> = P extends Builtin
+  ? P
+  : P & { [K in keyof P]: Exact<P[K], I[K]> } & Record<Exclude<keyof I, KeysOfUnion<P>>, never>;
+
 function longToNumber(long: Long): number {
   if (long.gt(Number.MAX_SAFE_INTEGER)) {
     throw new globalThis.Error('Value is larger than Number.MAX_SAFE_INTEGER');
diff --git a/integration/use-date-string/use-date-string.ts b/integration/use-date-string/use-date-string.ts
index d7e15656f..84b08b4cc 100644
--- a/integration/use-date-string/use-date-string.ts
+++ b/integration/use-date-string/use-date-string.ts
@@ -114,11 +114,11 @@ export const Todo = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Todo>): Todo {
+  fromPartial<I extends Exact<DeepPartial<Todo>, I>>(object: I): Todo {
     const message = { ...baseTodo } as Todo;
     message.id = object.id ?? '';
     message.timestamp = object.timestamp ?? undefined;
-    message.repeatedTimestamp = (object.repeatedTimestamp ?? []).map((e) => e);
+    message.repeatedTimestamp = object.repeatedTimestamp?.map((e) => e) || [];
     message.optionalTimestamp = object.optionalTimestamp ?? undefined;
     message.mapOfTimestamps = Object.entries(object.mapOfTimestamps ?? {}).reduce<{ [key: string]: string }>(
       (acc, [key, value]) => {
@@ -181,7 +181,7 @@ export const Todo_MapOfTimestampsEntry = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Todo_MapOfTimestampsEntry>): Todo_MapOfTimestampsEntry {
+  fromPartial<I extends Exact<DeepPartial<Todo_MapOfTimestampsEntry>, I>>(object: I): Todo_MapOfTimestampsEntry {
     const message = { ...baseTodo_MapOfTimestampsEntry } as Todo_MapOfTimestampsEntry;
     message.key = object.key ?? '';
     message.value = object.value ?? undefined;
@@ -190,6 +190,7 @@ export const Todo_MapOfTimestampsEntry = {
 };
 
 type Builtin = Date | Function | Uint8Array | string | number | boolean | undefined;
+
 export type DeepPartial<T> = T extends Builtin
   ? T
   : T extends Array<infer U>
@@ -200,6 +201,11 @@ export type DeepPartial<T> = T extends Builtin
   ? { [K in keyof T]?: DeepPartial<T[K]> }
   : Partial<T>;
 
+type KeysOfUnion<T> = T extends T ? keyof T : never;
+export type Exact<P, I extends P> = P extends Builtin
+  ? P
+  : P & { [K in keyof P]: Exact<P[K], I[K]> } & Record<Exclude<keyof I, KeysOfUnion<P>>, never>;
+
 function toTimestamp(dateStr: string): Timestamp {
   const date = new Date(dateStr);
   const seconds = date.getTime() / 1_000;
diff --git a/integration/use-date-true/google/protobuf/timestamp.ts b/integration/use-date-true/google/protobuf/timestamp.ts
index e4600a73e..0670c17fd 100644
--- a/integration/use-date-true/google/protobuf/timestamp.ts
+++ b/integration/use-date-true/google/protobuf/timestamp.ts
@@ -161,7 +161,7 @@ export const Timestamp = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Timestamp>): Timestamp {
+  fromPartial<I extends Exact<DeepPartial<Timestamp>, I>>(object: I): Timestamp {
     const message = { ...baseTimestamp } as Timestamp;
     message.seconds = object.seconds ?? 0;
     message.nanos = object.nanos ?? 0;
@@ -181,6 +181,7 @@ var globalThis: any = (() => {
 })();
 
 type Builtin = Date | Function | Uint8Array | string | number | boolean | undefined;
+
 export type DeepPartial<T> = T extends Builtin
   ? T
   : T extends Array<infer U>
@@ -191,6 +192,11 @@ export type DeepPartial<T> = T extends Builtin
   ? { [K in keyof T]?: DeepPartial<T[K]> }
   : Partial<T>;
 
+type KeysOfUnion<T> = T extends T ? keyof T : never;
+export type Exact<P, I extends P> = P extends Builtin
+  ? P
+  : P & { [K in keyof P]: Exact<P[K], I[K]> } & Record<Exclude<keyof I, KeysOfUnion<P>>, never>;
+
 function longToNumber(long: Long): number {
   if (long.gt(Number.MAX_SAFE_INTEGER)) {
     throw new globalThis.Error('Value is larger than Number.MAX_SAFE_INTEGER');
diff --git a/integration/use-date-true/use-date-true.ts b/integration/use-date-true/use-date-true.ts
index 172e251c7..2ce6aa5b6 100644
--- a/integration/use-date-true/use-date-true.ts
+++ b/integration/use-date-true/use-date-true.ts
@@ -114,11 +114,11 @@ export const Todo = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Todo>): Todo {
+  fromPartial<I extends Exact<DeepPartial<Todo>, I>>(object: I): Todo {
     const message = { ...baseTodo } as Todo;
     message.id = object.id ?? '';
     message.timestamp = object.timestamp ?? undefined;
-    message.repeatedTimestamp = (object.repeatedTimestamp ?? []).map((e) => e);
+    message.repeatedTimestamp = object.repeatedTimestamp?.map((e) => e) || [];
     message.optionalTimestamp = object.optionalTimestamp ?? undefined;
     message.mapOfTimestamps = Object.entries(object.mapOfTimestamps ?? {}).reduce<{ [key: string]: Date }>(
       (acc, [key, value]) => {
@@ -181,7 +181,7 @@ export const Todo_MapOfTimestampsEntry = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Todo_MapOfTimestampsEntry>): Todo_MapOfTimestampsEntry {
+  fromPartial<I extends Exact<DeepPartial<Todo_MapOfTimestampsEntry>, I>>(object: I): Todo_MapOfTimestampsEntry {
     const message = { ...baseTodo_MapOfTimestampsEntry } as Todo_MapOfTimestampsEntry;
     message.key = object.key ?? '';
     message.value = object.value ?? undefined;
@@ -190,6 +190,7 @@ export const Todo_MapOfTimestampsEntry = {
 };
 
 type Builtin = Date | Function | Uint8Array | string | number | boolean | undefined;
+
 export type DeepPartial<T> = T extends Builtin
   ? T
   : T extends Array<infer U>
@@ -200,6 +201,11 @@ export type DeepPartial<T> = T extends Builtin
   ? { [K in keyof T]?: DeepPartial<T[K]> }
   : Partial<T>;
 
+type KeysOfUnion<T> = T extends T ? keyof T : never;
+export type Exact<P, I extends P> = P extends Builtin
+  ? P
+  : P & { [K in keyof P]: Exact<P[K], I[K]> } & Record<Exclude<keyof I, KeysOfUnion<P>>, never>;
+
 function toTimestamp(date: Date): Timestamp {
   const seconds = date.getTime() / 1_000;
   const nanos = (date.getTime() % 1_000) * 1_000_000;
diff --git a/integration/value/google/protobuf/struct.ts b/integration/value/google/protobuf/struct.ts
index a2b7d6f54..28fe05424 100644
--- a/integration/value/google/protobuf/struct.ts
+++ b/integration/value/google/protobuf/struct.ts
@@ -147,7 +147,7 @@ export const Struct = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Struct>): Struct {
+  fromPartial<I extends Exact<DeepPartial<Struct>, I>>(object: I): Struct {
     const message = { ...baseStruct } as Struct;
     message.fields = Object.entries(object.fields ?? {}).reduce<{ [key: string]: any | undefined }>(
       (acc, [key, value]) => {
@@ -228,7 +228,7 @@ export const Struct_FieldsEntry = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Struct_FieldsEntry>): Struct_FieldsEntry {
+  fromPartial<I extends Exact<DeepPartial<Struct_FieldsEntry>, I>>(object: I): Struct_FieldsEntry {
     const message = { ...baseStruct_FieldsEntry } as Struct_FieldsEntry;
     message.key = object.key ?? '';
     message.value = object.value ?? undefined;
@@ -321,7 +321,7 @@ export const Value = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Value>): Value {
+  fromPartial<I extends Exact<DeepPartial<Value>, I>>(object: I): Value {
     const message = { ...baseValue } as Value;
     message.nullValue = object.nullValue ?? undefined;
     message.numberValue = object.numberValue ?? undefined;
@@ -414,9 +414,9 @@ export const ListValue = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<ListValue>): ListValue {
+  fromPartial<I extends Exact<DeepPartial<ListValue>, I>>(object: I): ListValue {
     const message = { ...baseListValue } as ListValue;
-    message.values = (object.values ?? []).map((e) => e);
+    message.values = object.values?.map((e) => e) || [];
     return message;
   },
 
@@ -430,6 +430,7 @@ export const ListValue = {
 };
 
 type Builtin = Date | Function | Uint8Array | string | number | boolean | undefined;
+
 export type DeepPartial<T> = T extends Builtin
   ? T
   : T extends Array<infer U>
@@ -440,6 +441,11 @@ export type DeepPartial<T> = T extends Builtin
   ? { [K in keyof T]?: DeepPartial<T[K]> }
   : Partial<T>;
 
+type KeysOfUnion<T> = T extends T ? keyof T : never;
+export type Exact<P, I extends P> = P extends Builtin
+  ? P
+  : P & { [K in keyof P]: Exact<P[K], I[K]> } & Record<Exclude<keyof I, KeysOfUnion<P>>, never>;
+
 // If you get a compile-error about 'Constructor<Long> and ... have no overlap',
 // add '--ts_proto_opt=esModuleInterop=true' as a flag when calling 'protoc'.
 if (util.Long !== Long) {
diff --git a/integration/value/google/protobuf/wrappers.ts b/integration/value/google/protobuf/wrappers.ts
index 216285744..35b159990 100644
--- a/integration/value/google/protobuf/wrappers.ts
+++ b/integration/value/google/protobuf/wrappers.ts
@@ -134,7 +134,7 @@ export const DoubleValue = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<DoubleValue>): DoubleValue {
+  fromPartial<I extends Exact<DeepPartial<DoubleValue>, I>>(object: I): DoubleValue {
     const message = { ...baseDoubleValue } as DoubleValue;
     message.value = object.value ?? 0;
     return message;
@@ -181,7 +181,7 @@ export const FloatValue = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<FloatValue>): FloatValue {
+  fromPartial<I extends Exact<DeepPartial<FloatValue>, I>>(object: I): FloatValue {
     const message = { ...baseFloatValue } as FloatValue;
     message.value = object.value ?? 0;
     return message;
@@ -228,7 +228,7 @@ export const Int64Value = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Int64Value>): Int64Value {
+  fromPartial<I extends Exact<DeepPartial<Int64Value>, I>>(object: I): Int64Value {
     const message = { ...baseInt64Value } as Int64Value;
     message.value = object.value ?? 0;
     return message;
@@ -275,7 +275,7 @@ export const UInt64Value = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<UInt64Value>): UInt64Value {
+  fromPartial<I extends Exact<DeepPartial<UInt64Value>, I>>(object: I): UInt64Value {
     const message = { ...baseUInt64Value } as UInt64Value;
     message.value = object.value ?? 0;
     return message;
@@ -322,7 +322,7 @@ export const Int32Value = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Int32Value>): Int32Value {
+  fromPartial<I extends Exact<DeepPartial<Int32Value>, I>>(object: I): Int32Value {
     const message = { ...baseInt32Value } as Int32Value;
     message.value = object.value ?? 0;
     return message;
@@ -369,7 +369,7 @@ export const UInt32Value = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<UInt32Value>): UInt32Value {
+  fromPartial<I extends Exact<DeepPartial<UInt32Value>, I>>(object: I): UInt32Value {
     const message = { ...baseUInt32Value } as UInt32Value;
     message.value = object.value ?? 0;
     return message;
@@ -416,7 +416,7 @@ export const BoolValue = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<BoolValue>): BoolValue {
+  fromPartial<I extends Exact<DeepPartial<BoolValue>, I>>(object: I): BoolValue {
     const message = { ...baseBoolValue } as BoolValue;
     message.value = object.value ?? false;
     return message;
@@ -463,7 +463,7 @@ export const StringValue = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<StringValue>): StringValue {
+  fromPartial<I extends Exact<DeepPartial<StringValue>, I>>(object: I): StringValue {
     const message = { ...baseStringValue } as StringValue;
     message.value = object.value ?? '';
     return message;
@@ -513,7 +513,7 @@ export const BytesValue = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<BytesValue>): BytesValue {
+  fromPartial<I extends Exact<DeepPartial<BytesValue>, I>>(object: I): BytesValue {
     const message = { ...baseBytesValue } as BytesValue;
     message.value = object.value ?? new Uint8Array();
     return message;
@@ -553,6 +553,7 @@ function base64FromBytes(arr: Uint8Array): string {
 }
 
 type Builtin = Date | Function | Uint8Array | string | number | boolean | undefined;
+
 export type DeepPartial<T> = T extends Builtin
   ? T
   : T extends Array<infer U>
@@ -563,6 +564,11 @@ export type DeepPartial<T> = T extends Builtin
   ? { [K in keyof T]?: DeepPartial<T[K]> }
   : Partial<T>;
 
+type KeysOfUnion<T> = T extends T ? keyof T : never;
+export type Exact<P, I extends P> = P extends Builtin
+  ? P
+  : P & { [K in keyof P]: Exact<P[K], I[K]> } & Record<Exclude<keyof I, KeysOfUnion<P>>, never>;
+
 function longToNumber(long: Long): number {
   if (long.gt(Number.MAX_SAFE_INTEGER)) {
     throw new globalThis.Error('Value is larger than Number.MAX_SAFE_INTEGER');
diff --git a/integration/value/value.ts b/integration/value/value.ts
index 0b7df9ffb..80f89d0d6 100644
--- a/integration/value/value.ts
+++ b/integration/value/value.ts
@@ -72,16 +72,17 @@ export const ValueMessage = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<ValueMessage>): ValueMessage {
+  fromPartial<I extends Exact<DeepPartial<ValueMessage>, I>>(object: I): ValueMessage {
     const message = { ...baseValueMessage } as ValueMessage;
     message.value = object.value ?? undefined;
     message.anyList = object.anyList ?? undefined;
-    message.repeatedAny = (object.repeatedAny ?? []).map((e) => e);
+    message.repeatedAny = object.repeatedAny?.map((e) => e) || [];
     return message;
   },
 };
 
 type Builtin = Date | Function | Uint8Array | string | number | boolean | undefined;
+
 export type DeepPartial<T> = T extends Builtin
   ? T
   : T extends Array<infer U>
@@ -92,6 +93,11 @@ export type DeepPartial<T> = T extends Builtin
   ? { [K in keyof T]?: DeepPartial<T[K]> }
   : Partial<T>;
 
+type KeysOfUnion<T> = T extends T ? keyof T : never;
+export type Exact<P, I extends P> = P extends Builtin
+  ? P
+  : P & { [K in keyof P]: Exact<P[K], I[K]> } & Record<Exclude<keyof I, KeysOfUnion<P>>, never>;
+
 // If you get a compile-error about 'Constructor<Long> and ... have no overlap',
 // add '--ts_proto_opt=esModuleInterop=true' as a flag when calling 'protoc'.
 if (util.Long !== Long) {
diff --git a/integration/vector-tile/vector_tile.ts b/integration/vector-tile/vector_tile.ts
index 703a38a34..3ad16effe 100644
--- a/integration/vector-tile/vector_tile.ts
+++ b/integration/vector-tile/vector_tile.ts
@@ -123,9 +123,9 @@ export const Tile = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Tile>): Tile {
+  fromPartial<I extends Exact<DeepPartial<Tile>, I>>(object: I): Tile {
     const message = { ...baseTile } as Tile;
-    message.layers = (object.layers ?? []).map((e) => Tile_Layer.fromPartial(e));
+    message.layers = object.layers?.map((e) => Tile_Layer.fromPartial(e)) || [];
     return message;
   },
 };
@@ -228,7 +228,7 @@ export const Tile_Value = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Tile_Value>): Tile_Value {
+  fromPartial<I extends Exact<DeepPartial<Tile_Value>, I>>(object: I): Tile_Value {
     const message = { ...baseTile_Value } as Tile_Value;
     message.stringValue = object.stringValue ?? '';
     message.floatValue = object.floatValue ?? 0;
@@ -333,12 +333,12 @@ export const Tile_Feature = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Tile_Feature>): Tile_Feature {
+  fromPartial<I extends Exact<DeepPartial<Tile_Feature>, I>>(object: I): Tile_Feature {
     const message = { ...baseTile_Feature } as Tile_Feature;
     message.id = object.id ?? 0;
-    message.tags = (object.tags ?? []).map((e) => e);
+    message.tags = object.tags?.map((e) => e) || [];
     message.type = object.type ?? 0;
-    message.geometry = (object.geometry ?? []).map((e) => e);
+    message.geometry = object.geometry?.map((e) => e) || [];
     return message;
   },
 };
@@ -438,13 +438,13 @@ export const Tile_Layer = {
     return obj;
   },
 
-  fromPartial(object: DeepPartial<Tile_Layer>): Tile_Layer {
+  fromPartial<I extends Exact<DeepPartial<Tile_Layer>, I>>(object: I): Tile_Layer {
     const message = { ...baseTile_Layer } as Tile_Layer;
     message.version = object.version ?? 0;
     message.name = object.name ?? '';
-    message.features = (object.features ?? []).map((e) => Tile_Feature.fromPartial(e));
-    message.keys = (object.keys ?? []).map((e) => e);
-    message.values = (object.values ?? []).map((e) => Tile_Value.fromPartial(e));
+    message.features = object.features?.map((e) => Tile_Feature.fromPartial(e)) || [];
+    message.keys = object.keys?.map((e) => e) || [];
+    message.values = object.values?.map((e) => Tile_Value.fromPartial(e)) || [];
     message.extent = object.extent ?? 0;
     return message;
   },
@@ -462,6 +462,7 @@ var globalThis: any = (() => {
 })();
 
 type Builtin = Date | Function | Uint8Array | string | number | boolean | undefined;
+
 export type DeepPartial<T> = T extends Builtin
   ? T
   : T extends Array<infer U>
@@ -472,6 +473,11 @@ export type DeepPartial<T> = T extends Builtin
   ? { [K in keyof T]?: DeepPartial<T[K]> }
   : Partial<T>;
 
+type KeysOfUnion<T> = T extends T ? keyof T : never;
+export type Exact<P, I extends P> = P extends Builtin
+  ? P
+  : P & { [K in keyof P]: Exact<P[K], I[K]> } & Record<Exclude<keyof I, KeysOfUnion<P>>, never>;
+
 function longToNumber(long: Long): number {
   if (long.gt(Number.MAX_SAFE_INTEGER)) {
     throw new globalThis.Error('Value is larger than Number.MAX_SAFE_INTEGER');
diff --git a/src/generate-type-registry.ts b/src/generate-type-registry.ts
index 4f1c0a7a8..1ee8fd999 100644
--- a/src/generate-type-registry.ts
+++ b/src/generate-type-registry.ts
@@ -17,7 +17,7 @@ export function generateTypeRegistry(ctx: Context): Code {
     export const messageTypeRegistry = new Map<string, MessageType>();
   `);
 
-  chunks.push(code`${ctx.utils.DeepPartial.ifUsed}`);
+  chunks.push(code` ${ctx.utils.Builtin.ifUsed} ${ctx.utils.DeepPartial.ifUsed}`);
 
   return joinCode(chunks, { on: '\n\n' });
 }
diff --git a/src/main.ts b/src/main.ts
index 8b7ddb02c..0f1fa60d3 100644
--- a/src/main.ts
+++ b/src/main.ts
@@ -417,14 +417,31 @@ function makeDeepPartial(options: Options, longs: ReturnType<typeof makeLongUtil
   // Allow passing longs as numbers or strings, nad we'll convert them
   const maybeLong =
     options.forceLong === LongOption.LONG ? code` : T extends ${longs.Long} ? string | number | Long ` : '';
-  const keys = options.outputTypeRegistry ? code`Exclude<keyof T, '$type'>` : code`keyof T`;
+
+  const Builtin = conditionalOutput(
+    'Builtin',
+    code`type Builtin = Date | Function | Uint8Array | string | number | boolean | undefined;`
+  );
+
+  // Based on https://github.com/sindresorhus/type-fest/pull/259
+  const maybeExcludeType = options.outputTypeRegistry ? `| '$type'` : '';
+  const Exact = conditionalOutput(
+    'Exact',
+    code`
+      type KeysOfUnion<T> = T extends T ? keyof T : never;
+      ${maybeExport} type Exact<P, I extends P> = P extends ${Builtin}
+        ? P
+        : P &
+        { [K in keyof P]: Exact<P[K], I[K]> } & Record<Exclude<keyof I, KeysOfUnion<P> ${maybeExcludeType}>, never>;
+    `
+  );
 
   // Based on the type from ts-essentials
+  const keys = options.outputTypeRegistry ? code`Exclude<keyof T, '$type'>` : code`keyof T`;
   const DeepPartial = conditionalOutput(
     'DeepPartial',
     code`
-      type Builtin = Date | Function | Uint8Array | string | number | boolean | undefined;
-      ${maybeExport} type DeepPartial<T> =  T extends Builtin
+      ${maybeExport} type DeepPartial<T> =  T extends ${Builtin}
         ? T
         ${maybeLong}
         : T extends Array<infer U>
@@ -437,7 +454,7 @@ function makeDeepPartial(options: Options, longs: ReturnType<typeof makeLongUtil
     `
   );
 
-  return { DeepPartial };
+  return { Builtin, DeepPartial, Exact };
 }
 
 function makeTimestampMethods(options: Options, longs: ReturnType<typeof makeLongUtils>) {
@@ -1187,8 +1204,9 @@ function generateFromPartial(ctx: Context, fullName: string, messageDesc: Descri
   const Timestamp = imp('Timestamp@./google/protobuf/timestamp');
 
   // create the basic function declaration
+  const paramName = messageDesc.field.length > 0 ? 'object' : '_';
   chunks.push(code`
-    fromPartial(${messageDesc.field.length > 0 ? 'object' : '_'}: ${utils.DeepPartial}<${fullName}>): ${fullName} {
+    fromPartial<I extends ${utils.Exact}<${utils.DeepPartial}<${fullName}>, I>>(${paramName}: I): ${fullName} {
       const message = { ...base${fullName} } as ${fullName};
   `);
 
@@ -1258,7 +1276,7 @@ function generateFromPartial(ctx: Context, fullName: string, messageDesc: Descri
         `);
       } else {
         chunks.push(code`
-          message.${fieldName} = (object.${fieldName} ?? []).map((e) => ${readSnippet('e')});
+          message.${fieldName} = object.${fieldName}?.map((e) => ${readSnippet('e')}) || [];
         `);
       }
     } else if (isWithinOneOfThatShouldBeUnion(options, field)) {