diff --git a/src/type/definition.js b/src/type/definition.js
index d75a15a731..7b73804670 100644
--- a/src/type/definition.js
+++ b/src/type/definition.js
@@ -563,7 +563,7 @@ export type GraphQLTypeResolver<TSource, TContext> = (
   value: TSource,
   context: TContext,
   info: GraphQLResolveInfo
-) => ?GraphQLObjectType | ?string | ?Promise<?GraphQLObjectType | ?string>;
+) => ?GraphQLObjectType | string | Promise<?GraphQLObjectType | string>;
 
 export type GraphQLIsTypeOfFn<TSource, TContext> = (
   source: TSource,