diff --git a/lib/fetch/response.js b/lib/fetch/response.js
index 018224bc02c..be97d67ce6f 100644
--- a/lib/fetch/response.js
+++ b/lib/fetch/response.js
@@ -48,7 +48,7 @@ class Response {
   }
 
   // https://fetch.spec.whatwg.org/#dom-response-json
-  static json (data, init = {}) {
+  static json (data = undefined, init = {}) {
     if (arguments.length === 0) {
       throw new TypeError(
         'Failed to execute \'json\' on \'Response\': 1 argument required, but 0 present.'
diff --git a/test/wpt/status/fetch.status.json b/test/wpt/status/fetch.status.json
index c432144f217..7c37163c35a 100644
--- a/test/wpt/status/fetch.status.json
+++ b/test/wpt/status/fetch.status.json
@@ -23,8 +23,7 @@
 		]
 	},
 	"idlharness.any.js": {
-		"fail": [
-			"Response interface: operation json(any, optional ResponseInit)",
+		"flaky": [
 			"Window interface: operation fetch(RequestInfo, optional RequestInit)"
 		]
 	},