diff --git a/src/execution/execute.js b/src/execution/execute.js
index 29e9de0e97..ecf3cff3f2 100644
--- a/src/execution/execute.js
+++ b/src/execution/execute.js
@@ -117,11 +117,6 @@ export function execute(
   operationName?: ?string
 ): Promise<ExecutionResult> {
   invariant(schema, 'Must provide schema');
-  invariant(
-    schema instanceof GraphQLSchema,
-    'Schema must be an instance of GraphQLSchema. Also ensure that there are ' +
-    'not multiple versions of GraphQL installed in your node_modules directory.'
-  );
 
   // If a valid context cannot be created due to incorrect arguments,
   // this will throw an error.
diff --git a/src/utilities/extendSchema.js b/src/utilities/extendSchema.js
index 2a7f57a75d..2b2b9db7aa 100644
--- a/src/utilities/extendSchema.js
+++ b/src/utilities/extendSchema.js
@@ -94,10 +94,6 @@ export function extendSchema(
   schema: GraphQLSchema,
   documentAST: Document
 ): GraphQLSchema {
-  invariant(
-    schema instanceof GraphQLSchema,
-    'Must provide valid GraphQLSchema'
-  );
 
   invariant(
     documentAST && documentAST.kind === DOCUMENT,
diff --git a/src/validation/validate.js b/src/validation/validate.js
index b601e79042..e22ffbf46e 100644
--- a/src/validation/validate.js
+++ b/src/validation/validate.js
@@ -53,11 +53,6 @@ export function validate(
 ): Array<GraphQLError> {
   invariant(schema, 'Must provide schema');
   invariant(ast, 'Must provide document');
-  invariant(
-    schema instanceof GraphQLSchema,
-    'Schema must be an instance of GraphQLSchema. Also ensure that there are ' +
-    'not multiple versions of GraphQL installed in your node_modules directory.'
-  );
   const typeInfo = new TypeInfo(schema);
   return visitUsingRules(schema, typeInfo, ast, rules || specifiedRules);
 }