diff --git a/components/script/dom/webidls/Event.webidl b/components/script/dom/webidls/Event.webidl
index 9aea7e38e75..6c7861ecc6e 100644
--- a/components/script/dom/webidls/Event.webidl
+++ b/components/script/dom/webidls/Event.webidl
@@ -35,7 +35,7 @@ interface Event {
   [Constant]
   readonly attribute DOMTimeStamp timeStamp;
 
-  void initEvent(DOMString type, boolean bubbles, boolean cancelable);
+  void initEvent(DOMString type, optional boolean bubbles = false, optional boolean cancelable = false);
 };
 
 dictionary EventInit {
diff --git a/tests/wpt/metadata/dom/events/Event-initEvent.html.ini b/tests/wpt/metadata/dom/events/Event-initEvent.html.ini
index 2003c8b61c4..f7a1e9dc18c 100644
--- a/tests/wpt/metadata/dom/events/Event-initEvent.html.ini
+++ b/tests/wpt/metadata/dom/events/Event-initEvent.html.ini
@@ -3,9 +3,6 @@
   [Calling initEvent must unset the stop propagation flag.]
     expected: FAIL
 
-  [Tests initEvent's default parameter values.]
-    expected: FAIL
-
   [Properties of initEvent(type, true, true)]
     expected: FAIL
 
diff --git a/tests/wpt/metadata/dom/interfaces.html.ini b/tests/wpt/metadata/dom/interfaces.html.ini
index b94d68781c3..b0bff18aa60 100644
--- a/tests/wpt/metadata/dom/interfaces.html.ini
+++ b/tests/wpt/metadata/dom/interfaces.html.ini
@@ -878,9 +878,6 @@
   [Event interface: attribute composed]
     expected: FAIL
 
-  [Event interface: operation initEvent(DOMString, boolean, boolean)]
-    expected: FAIL
-
   [Event interface: document.createEvent("Event") must inherit property "srcElement" with the proper type]
     expected: FAIL