diff --git a/src/utilities/buildASTSchema.js b/src/utilities/buildASTSchema.js
index 21dc318eb4..7f13c15787 100644
--- a/src/utilities/buildASTSchema.js
+++ b/src/utilities/buildASTSchema.js
@@ -506,7 +506,7 @@ function getLeadingCommentBlock(node): void | string {
  */
 export function buildSchema(
   source: string | Source,
-  options: BuildSchemaOptions & ParseOptions,
+  options?: BuildSchemaOptions & ParseOptions,
 ): GraphQLSchema {
   return buildASTSchema(parse(source, options), options);
 }