diff --git a/packages/graphql-modules/src/module/resolvers.ts b/packages/graphql-modules/src/module/resolvers.ts
index f74bebcc99..374a53a8ce 100644
--- a/packages/graphql-modules/src/module/resolvers.ts
+++ b/packages/graphql-modules/src/module/resolvers.ts
@@ -5,6 +5,7 @@ import {
   defaultFieldResolver,
   FieldNode,
   GraphQLResolveInfo,
+  isScalarType,
 } from 'graphql';
 import { Resolvers, ModuleConfig } from './types';
 import { ModuleMetadata } from './metadata';
@@ -508,7 +509,7 @@ function isResolveOptions(value: any): value is ResolveOptions {
 }
 
 function isScalarResolver(obj: any): obj is GraphQLScalarType {
-  return obj instanceof GraphQLScalarType;
+  return isScalarType(obj);
 }
 
 interface EnumResolver {
diff --git a/packages/graphql-modules/src/shared/utils.ts b/packages/graphql-modules/src/shared/utils.ts
index 3c63175788..20515269bd 100644
--- a/packages/graphql-modules/src/shared/utils.ts
+++ b/packages/graphql-modules/src/shared/utils.ts
@@ -1,4 +1,4 @@
-import { GraphQLSchema } from 'graphql';
+import { GraphQLSchema, isSchema } from 'graphql';
 
 export function flatten<T>(arr: T[]): T extends (infer A)[] ? A[] : T[] {
   return Array.prototype.concat(...arr) as any;
@@ -105,7 +105,7 @@ export function uniqueId(isNotUsed: (id: string) => boolean) {
 }
 
 export function isNotSchema<T>(obj: any): obj is T {
-  return obj instanceof GraphQLSchema === false;
+  return !isSchema(obj);
 }
 
 export function merge<S extends object, T extends object>(