diff --git a/components/script/dom/bindings/codegen/CodegenRust.py b/components/script/dom/bindings/codegen/CodegenRust.py
index 7610b8442b4d..fe3398417b2c 100644
--- a/components/script/dom/bindings/codegen/CodegenRust.py
+++ b/components/script/dom/bindings/codegen/CodegenRust.py
@@ -6425,7 +6425,8 @@ def struct(self):
         mustRoot = ""
         if self.membersNeedTracing():
             mustRoot = "#[unrooted_must_root_lint::must_root]\n"
-            derive += ["Default"]
+            if not self.hasRequiredFields(self.dictionary):
+                derive += ["Default"]
 
         return (string.Template(
                 "#[derive(${derive})]\n"
@@ -6485,16 +6486,14 @@ def memberInsert(memberInfo):
         selfName = self.makeClassName(d)
         if self.membersNeedTracing():
             actualType = "RootedTraceableBox<%s>" % selfName
-            preInitial = "let mut dictionary = RootedTraceableBox::new(%s::default());\n" % selfName
-            initParent = initParent = ("dictionary.parent = %s;\n" % initParent) if initParent else ""
-            memberInits = CGList([memberInit(m, False) for m in self.memberInfo])
-            postInitial = ""
+            preInitial = "let dictionary = RootedTraceableBox::new(%s {\n" % selfName
+            postInitial = "});\n"
         else:
             actualType = selfName
             preInitial = "let dictionary = %s {\n" % selfName
             postInitial = "};\n"
-            initParent = ("parent: %s,\n" % initParent) if initParent else ""
-            memberInits = CGList([memberInit(m, True) for m in self.memberInfo])
+        initParent = ("parent: %s,\n" % initParent) if initParent else ""
+        memberInits = CGList([memberInit(m, True) for m in self.memberInfo])
 
         return string.Template(
             "impl ${selfName} {\n"
@@ -6540,8 +6539,8 @@ def memberInsert(memberInfo):
                 "initParent": CGIndenter(CGGeneric(initParent), indentLevel=16).define(),
                 "initMembers": CGIndenter(memberInits, indentLevel=16).define(),
                 "insertMembers": CGIndenter(memberInserts, indentLevel=8).define(),
-                "preInitial": CGIndenter(CGGeneric(preInitial), indentLevel=16).define(),
-                "postInitial": CGIndenter(CGGeneric(postInitial), indentLevel=16).define(),
+                "preInitial": CGIndenter(CGGeneric(preInitial), indentLevel=8).define(),
+                "postInitial": CGIndenter(CGGeneric(postInitial), indentLevel=8).define(),
             })
 
     def membersNeedTracing(self):
diff --git a/components/script/dom/promiserejectionevent.rs b/components/script/dom/promiserejectionevent.rs
index 4e4a148905a9..19bf96b9b12f 100644
--- a/components/script/dom/promiserejectionevent.rs
+++ b/components/script/dom/promiserejectionevent.rs
@@ -5,7 +5,7 @@
 use crate::dom::bindings::codegen::Bindings::EventBinding::EventMethods;
 use crate::dom::bindings::codegen::Bindings::PromiseRejectionEventBinding;
 use crate::dom::bindings::codegen::Bindings::PromiseRejectionEventBinding::PromiseRejectionEventMethods;
-use crate::dom::bindings::error::{Error, Fallible};
+use crate::dom::bindings::error::Fallible;
 use crate::dom::bindings::inheritance::Castable;
 use crate::dom::bindings::reflector::reflect_dom_object;
 use crate::dom::bindings::root::DomRoot;
@@ -72,14 +72,7 @@ impl PromiseRejectionEvent {
         init: RootedTraceableBox<PromiseRejectionEventBinding::PromiseRejectionEventInit>,
     ) -> Fallible<DomRoot<Self>> {
         let reason = init.reason.handle();
-        let promise = match init.promise.as_ref() {
-            Some(promise) => promise.clone(),
-            None => {
-                return Err(Error::Type(
-                    "required member promise is undefined.".to_string(),
-                ));
-            },
-        };
+        let promise = init.promise.clone();
         let bubbles = EventBubbles::from(init.parent.bubbles);
         let cancelable = EventCancelable::from(init.parent.cancelable);
 
diff --git a/components/script/dom/webidls/PromiseRejectionEvent.webidl b/components/script/dom/webidls/PromiseRejectionEvent.webidl
index 6ef93b8b1a7c..70d11b1ff33b 100644
--- a/components/script/dom/webidls/PromiseRejectionEvent.webidl
+++ b/components/script/dom/webidls/PromiseRejectionEvent.webidl
@@ -6,12 +6,12 @@
 
 [Exposed=(Window,Worker)]
 interface PromiseRejectionEvent : Event {
-  [Throws] constructor(DOMString type, optional PromiseRejectionEventInit eventInitDict = {});
+  [Throws] constructor(DOMString type, PromiseRejectionEventInit eventInitDict);
   readonly attribute Promise<any> promise;
   readonly attribute any reason;
 };
 
 dictionary PromiseRejectionEventInit : EventInit {
-  /* required */ Promise<any> promise;
+  required Promise<any> promise;
   any reason;
 };
diff --git a/tests/wpt/metadata/html/dom/idlharness.https.html.ini b/tests/wpt/metadata/html/dom/idlharness.https.html.ini
index dc99e0c09f1b..692dc849677f 100644
--- a/tests/wpt/metadata/html/dom/idlharness.https.html.ini
+++ b/tests/wpt/metadata/html/dom/idlharness.https.html.ini
@@ -1163,9 +1163,6 @@
   [OffscreenCanvasRenderingContext2D interface: operation closePath()]
     expected: FAIL
 
-  [PromiseRejectionEvent interface object length]
-    expected: FAIL
-
   [CanvasRenderingContext2D interface: document.createElement("canvas").getContext("2d") must inherit property "textAlign" with the proper type]
     expected: FAIL
 
diff --git a/tests/wpt/metadata/html/dom/idlharness.worker.js.ini b/tests/wpt/metadata/html/dom/idlharness.worker.js.ini
index 9fa9c825549f..518459adb811 100644
--- a/tests/wpt/metadata/html/dom/idlharness.worker.js.ini
+++ b/tests/wpt/metadata/html/dom/idlharness.worker.js.ini
@@ -68,9 +68,6 @@
   [OffscreenCanvasRenderingContext2D interface: operation restore()]
     expected: FAIL
 
-  [PromiseRejectionEvent interface object length]
-    expected: FAIL
-
   [WorkerGlobalScope interface: calling createImageBitmap(ImageBitmapSource, ImageBitmapOptions) on self with too few arguments must throw TypeError]
     expected: FAIL