diff --git a/packages/react-reconciler/src/ReactFiberClassUpdateQueue.js b/packages/react-reconciler/src/ReactFiberClassUpdateQueue.js
index a6148e0184198..2e88c982022d3 100644
--- a/packages/react-reconciler/src/ReactFiberClassUpdateQueue.js
+++ b/packages/react-reconciler/src/ReactFiberClassUpdateQueue.js
@@ -161,7 +161,7 @@ export const CaptureUpdate = 3;
 let hasForceUpdate = false;
 
 let didWarnUpdateInsideUpdate;
-let currentlyProcessingQueue;
+let currentlyProcessingQueue: ?SharedQueue<$FlowFixMe>;
 export let resetCurrentlyProcessingQueue: () => void;
 if (__DEV__) {
   didWarnUpdateInsideUpdate = false;
@@ -475,7 +475,6 @@ export function processUpdateQueue<State>(
   hasForceUpdate = false;
 
   if (__DEV__) {
-    // $FlowFixMe[escaped-generic] discovered when updating Flow
     currentlyProcessingQueue = queue.shared;
   }
 
diff --git a/packages/react-reconciler/src/ReactFiberHooks.js b/packages/react-reconciler/src/ReactFiberHooks.js
index 6741a55e4b42f..e9763f9fe289f 100644
--- a/packages/react-reconciler/src/ReactFiberHooks.js
+++ b/packages/react-reconciler/src/ReactFiberHooks.js
@@ -165,7 +165,7 @@ export type UpdateQueue<S, A> = {
 };
 
 let didWarnAboutMismatchedHooksForComponent;
-let didWarnUncachedGetSnapshot;
+let didWarnUncachedGetSnapshot: void | true;
 let didWarnAboutUseWrappedInTryCatch;
 if (__DEV__) {
   didWarnAboutMismatchedHooksForComponent = new Set<string | null>();
diff --git a/packages/react-refresh/src/ReactFreshRuntime.js b/packages/react-refresh/src/ReactFreshRuntime.js
index d81c1140cab95..c9706041ce1ff 100644
--- a/packages/react-refresh/src/ReactFreshRuntime.js
+++ b/packages/react-refresh/src/ReactFreshRuntime.js
@@ -642,8 +642,8 @@ export function createSignatureFunctionForTransform(): <T>(
   getCustomHooks?: () => Array<Function>,
 ) => T | void {
   if (__DEV__) {
-    let savedType;
-    let hasCustomHooks;
+    let savedType: mixed;
+    let hasCustomHooks: boolean;
     let didCollectHooks = false;
     return function <T>(
       type: T,
diff --git a/packages/react-server/src/ReactFlightServerConfigStream.js b/packages/react-server/src/ReactFlightServerConfigStream.js
index 889a856e49437..43a7f75c80681 100644
--- a/packages/react-server/src/ReactFlightServerConfigStream.js
+++ b/packages/react-server/src/ReactFlightServerConfigStream.js
@@ -126,6 +126,7 @@ export function processModelChunk(
   id: number,
   model: ReactModel,
 ): Chunk {
+  // $FlowFixMe[incompatible-type] stringify can return null
   const json: string = stringify(model, request.toJSON);
   const row = id.toString(16) + ':' + json + '\n';
   return stringToChunk(row);
@@ -146,6 +147,7 @@ export function processImportChunk(
   id: number,
   clientReferenceMetadata: ReactModel,
 ): Chunk {
+  // $FlowFixMe[incompatible-type] stringify can return null
   const json: string = stringify(clientReferenceMetadata);
   const row = serializeRowHeader('I', id) + json + '\n';
   return stringToChunk(row);