diff --git a/testing/web-platform/tests/interfaces/requestidlecallback.idl b/testing/web-platform/tests/interfaces/requestidlecallback.idl
index 812cc0ef8153..c763b50bde78 100644
--- a/testing/web-platform/tests/interfaces/requestidlecallback.idl
+++ b/testing/web-platform/tests/interfaces/requestidlecallback.idl
@@ -4,7 +4,7 @@
 // Source: Cooperative Scheduling of Background Tasks (https://w3c.github.io/requestidlecallback/)
 
 partial interface Window {
-  unsigned long requestIdleCallback(IdleRequestCallback callback, optional IdleRequestOptions options);
+  unsigned long requestIdleCallback(IdleRequestCallback callback, optional IdleRequestOptions options = {});
   void cancelIdleCallback(unsigned long handle);
 };