--- a/testing/web-platform/tests/interfaces/fetch.idl
+++ b/testing/web-platform/tests/interfaces/fetch.idl
@@ -22,17 +22,17 @@ interface mixin Body {
   [NewObject] Promise<ArrayBuffer> arrayBuffer();
   [NewObject] Promise<Blob> blob();
   [NewObject] Promise<FormData> formData();
   [NewObject] Promise<any> json();
   [NewObject] Promise<USVString> text();
 };
 typedef (Request or USVString) RequestInfo;
 
-[Constructor(RequestInfo input, optional RequestInit init),
+[Constructor(RequestInfo input, optional RequestInit init = {}),
  Exposed=(Window,Worker)]
 interface Request {
   readonly attribute ByteString method;
   readonly attribute USVString url;
   [SameObject] readonly attribute Headers headers;
 
   readonly attribute RequestDestination destination;
   readonly attribute USVString referrer;
@@ -67,17 +67,17 @@ dictionary RequestInit {
   any window; // can only be set to null
 };
 
 enum RequestDestination { "", "audio", "audioworklet", "document", "embed", "font", "image", "manifest", "object", "paintworklet", "report", "script", "sharedworker", "style",  "track", "video", "worker", "xslt" };
 enum RequestMode { "navigate", "same-origin", "no-cors", "cors" };
 enum RequestCredentials { "omit", "same-origin", "include" };
 enum RequestCache { "default", "no-store", "reload", "no-cache", "force-cache", "only-if-cached" };
 enum RequestRedirect { "follow", "error", "manual" };
-[Constructor(optional BodyInit? body = null, optional ResponseInit init), Exposed=(Window,Worker)]
+[Constructor(optional BodyInit? body = null, optional ResponseInit init = {}), Exposed=(Window,Worker)]
 interface Response {
   [NewObject] static Response error();
   [NewObject] static Response redirect(USVString url, optional unsigned short status = 302);
 
   readonly attribute ResponseType type;
 
   readonly attribute USVString url;
   readonly attribute boolean redirected;