diff --git a/src/utilities/__tests__/valueFromAST-test.js b/src/utilities/__tests__/valueFromAST-test.js
index b1436edf97..a444392777 100644
--- a/src/utilities/__tests__/valueFromAST-test.js
+++ b/src/utilities/__tests__/valueFromAST-test.js
@@ -29,7 +29,7 @@ describe('valueFromAST', () => {
   function expectValueFrom(
     valueText: string,
     type: GraphQLInputType,
-    variables: ?ObjMap<mixed>,
+    variables?: ObjMap<mixed>,
   ) {
     const ast = parseValue(valueText);
     const value = valueFromAST(ast, type, variables);