diff --git a/src/__tests__/lib.test.ts b/src/__tests__/lib.test.ts
index f8271d2..e9e780e 100644
--- a/src/__tests__/lib.test.ts
+++ b/src/__tests__/lib.test.ts
@@ -6,10 +6,31 @@ import schema from "./schema";
 
 describe("Automocking", () => {
   describe("Guardrails", () => {
-    test.todo("it throws without a schema");
-    test.todo("it throws without a valid schema");
-    test.todo("it throws without a query");
-    test.todo("it throws without a valid query");
+    test("it throws without a schema", () => {
+      expect(() => {
+        (ergonomock as any)();
+      }).toThrowError("Ergonomock requires a valid GraphQL schema");
+    });
+    test("it throws without a valid schema", () => {
+      expect(() => {
+        (ergonomock as any)("foo", "bar");
+      }).toThrowError("Ergonomock requires a valid GraphQL schema");
+    });
+    test("it throws without a query", () => {
+      expect(() => {
+        (ergonomock as any)(schema);
+      }).toThrowError("Ergonomock requires a GraphQL query, either as a string or DocumentNode.");
+    });
+    test("it throws without a parseable query", () => {
+      expect(() => {
+        (ergonomock as any)(schema, "asdasd");
+      }).toThrowError("Syntax Error: Unexpected Name");
+    });
+    test("it throws without a valid query", () => {
+      expect(() => {
+        (ergonomock as any)(schema, "query { fooBar }");
+      }).toThrowError('Cannot query field "fooBar" on type "RootQuery".');
+    });
   });
 
   describe("No provided mocks", () => {
@@ -670,7 +691,9 @@ describe("Automocking", () => {
           returnEnum
           returnBirdsAndBees {
             __typename
-            returnInt
+            ... on Flying {
+              returnInt
+            }
             ... on Bird {
               returnString
             }
@@ -933,7 +956,9 @@ describe("Automocking", () => {
         {
           returnBirdsAndBees {
             __typename
-            id
+            ... on Flying {
+              id
+            }
           }
           returnString
         }
diff --git a/src/mock.ts b/src/mock.ts
index 25404d5..404e936 100644
--- a/src/mock.ts
+++ b/src/mock.ts
@@ -14,7 +14,9 @@ import {
   GraphQLList,
   GraphQLEnumType,
   isObjectType,
-  DocumentNode
+  DocumentNode,
+  isSchema,
+  validate
 } from "graphql";
 
 import random from "./utils/random";
@@ -39,9 +41,24 @@ export function ergonomock(
   mocks?: ErgonoMockShape,
   mockSeed?: string
 ) {
-  random.seed(mockSeed);
+  // Guard rails for schema & query
+  if (!schema || !isSchema(schema)) {
+    throw new Error("Ergonomock requires a valid GraphQL schema.");
+  }
+
+  if (!query) {
+    throw new Error("Ergonomock requires a GraphQL query, either as a string or DocumentNode.");
+  }
+
   const document = typeof query === "string" ? parse(query) : query;
 
+  const errors = validate(schema, document);
+  if (errors.length) {
+    throw errors[0];
+  }
+
+  random.seed(mockSeed);
+
   const mockResolverFunction = function(
     type: GraphQLType,
     typeName?: string, // TODO: get rid of this?