diff --git a/Userland/Libraries/LibWeb/UIEvents/UIEvent.h b/Userland/Libraries/LibWeb/UIEvents/UIEvent.h
index 3393d0b2d6..d410922179 100644
--- a/Userland/Libraries/LibWeb/UIEvents/UIEvent.h
+++ b/Userland/Libraries/LibWeb/UIEvents/UIEvent.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2020, Andreas Kling <kling@serenityos.org>
+ * Copyright (c) 2020-2022, Andreas Kling <kling@serenityos.org>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -36,6 +36,13 @@ public:
     DOM::Window const* view() const { return m_view; }
     int detail() const { return m_detail; }
 
+    void init_ui_event(String const& type, bool bubbles, bool cancelable, DOM::Window* view, int detail)
+    {
+        init_event(type, bubbles, cancelable);
+        m_view = view;
+        m_detail = detail;
+    }
+
 protected:
     explicit UIEvent(FlyString const& event_name)
         : Event(event_name)
diff --git a/Userland/Libraries/LibWeb/UIEvents/UIEvent.idl b/Userland/Libraries/LibWeb/UIEvents/UIEvent.idl
index d317d3011a..94431c183f 100644
--- a/Userland/Libraries/LibWeb/UIEvents/UIEvent.idl
+++ b/Userland/Libraries/LibWeb/UIEvents/UIEvent.idl
@@ -4,6 +4,9 @@ interface UIEvent : Event {
     constructor(DOMString type, optional UIEventInit eventInitDict = {});
     readonly attribute Window? view;
     readonly attribute long detail;
+
+    // NOTE: This is "deprecated, but supported for backwards-compatibility with widely-deployed implementations."
+    [ImplementedAs=init_ui_event] undefined initUIEvent(DOMString typeArg, optional boolean bubblesArg = false, optional boolean cancelableArg = false, optional Window? viewArg = null, optional long detailArg = 0);
 };
 
 dictionary UIEventInit : EventInit {