diff --git a/Userland/Libraries/LibWeb/HTML/Window.cpp b/Userland/Libraries/LibWeb/HTML/Window.cpp
index f63472e5461..bf83d56ab1b 100644
--- a/Userland/Libraries/LibWeb/HTML/Window.cpp
+++ b/Userland/Libraries/LibWeb/HTML/Window.cpp
@@ -826,22 +826,6 @@ void Window::invoke_idle_callbacks()
     }
 }
 
-// https://w3c.github.io/requestidlecallback/#the-cancelidlecallback-method
-void Window::cancel_idle_callback_impl(u32 handle)
-{
-    // 1. Let window be this Window object.
-    auto& window = *this;
-    // 2. Find the entry in either the window's list of idle request callbacks or list of runnable idle callbacks
-    //    that is associated with the value handle.
-    // 3. If there is such an entry, remove it from both window's list of idle request callbacks and the list of runnable idle callbacks.
-    window.m_idle_request_callbacks.remove_first_matching([handle](auto& callback) {
-        return callback->handle() == handle;
-    });
-    window.m_runnable_idle_callbacks.remove_first_matching([handle](auto& callback) {
-        return callback->handle() == handle;
-    });
-}
-
 void Window::set_associated_document(DOM::Document& document)
 {
     m_associated_document = &document;
@@ -932,8 +916,6 @@ WebIDL::ExceptionOr<void> Window::initialize_web_interfaces(Badge<WindowEnvironm
 
     define_native_function(realm, "queueMicrotask", queue_microtask, 1, attr);
 
-    define_native_function(realm, "cancelIdleCallback", cancel_idle_callback, 1, attr);
-
     define_native_function(realm, "structuredClone", structured_clone, 1, attr);
 
     define_native_function(realm, "fetch", Bindings::fetch, 1, attr);
@@ -1480,6 +1462,22 @@ u32 Window::request_idle_callback(WebIDL::CallbackType& callback, RequestIdleCal
     (void)options;
 }
 
+// https://w3c.github.io/requestidlecallback/#dom-window-cancelidlecallback
+void Window::cancel_idle_callback(u32 handle)
+{
+    // 1. Let window be this Window object.
+
+    // 2. Find the entry in either the window's list of idle request callbacks or list of runnable idle callbacks
+    //    that is associated with the value handle.
+    // 3. If there is such an entry, remove it from both window's list of idle request callbacks and the list of runnable idle callbacks.
+    m_idle_request_callbacks.remove_first_matching([&](auto& callback) {
+        return callback->handle() == handle;
+    });
+    m_runnable_idle_callbacks.remove_first_matching([&](auto& callback) {
+        return callback->handle() == handle;
+    });
+}
+
 // https://w3c.github.io/selection-api/#dom-window-getselection
 JS::GCPtr<Selection::Selection> Window::get_selection() const
 {
@@ -1617,16 +1615,6 @@ JS_DEFINE_NATIVE_FUNCTION(Window::queue_microtask)
     return JS::js_undefined();
 }
 
-JS_DEFINE_NATIVE_FUNCTION(Window::cancel_idle_callback)
-{
-    auto* impl = TRY(impl_from(vm));
-    if (!vm.argument_count())
-        return vm.throw_completion<JS::TypeError>(JS::ErrorType::BadArgCountOne, "cancelIdleCallback");
-    auto id = TRY(vm.argument(0).to_u32(vm));
-    impl->cancel_idle_callback_impl(id);
-    return JS::js_undefined();
-}
-
 // https://html.spec.whatwg.org/multipage/window-object.html#number-of-document-tree-child-browsing-contexts
 size_t Window::document_tree_child_browsing_context_count() const
 {
diff --git a/Userland/Libraries/LibWeb/HTML/Window.h b/Userland/Libraries/LibWeb/HTML/Window.h
index e0dd30fd57a..1935e630185 100644
--- a/Userland/Libraries/LibWeb/HTML/Window.h
+++ b/Userland/Libraries/LibWeb/HTML/Window.h
@@ -120,8 +120,6 @@ public:
 
     void start_an_idle_period();
 
-    void cancel_idle_callback_impl(u32);
-
     AnimationFrameCallbackDriver& animation_frame_callback_driver() { return m_animation_frame_callback_driver; }
 
     // https://html.spec.whatwg.org/multipage/interaction.html#transient-activation
@@ -181,6 +179,7 @@ public:
     double device_pixel_ratio() const;
 
     u32 request_idle_callback(WebIDL::CallbackType&, RequestIdleCallback::IdleRequestOptions const&);
+    void cancel_idle_callback(u32 handle);
 
     JS::GCPtr<Selection::Selection> get_selection() const;
 
@@ -264,8 +263,6 @@ private:
 
     JS_DECLARE_NATIVE_FUNCTION(queue_microtask);
 
-    JS_DECLARE_NATIVE_FUNCTION(cancel_idle_callback);
-
     HTML::Location* m_location { nullptr };
 
     // [[CrossOriginPropertyDescriptorMap]], https://html.spec.whatwg.org/multipage/browsers.html#crossoriginpropertydescriptormap
diff --git a/Userland/Libraries/LibWeb/HTML/Window.idl b/Userland/Libraries/LibWeb/HTML/Window.idl
index 69f3a148159..08b093efd63 100644
--- a/Userland/Libraries/LibWeb/HTML/Window.idl
+++ b/Userland/Libraries/LibWeb/HTML/Window.idl
@@ -80,6 +80,7 @@ interface Window : EventTarget {
 
     // https://w3c.github.io/requestidlecallback/#window_extensions
     unsigned long requestIdleCallback(IdleRequestCallback callback, optional IdleRequestOptions options = {});
+    undefined cancelIdleCallback(unsigned long handle);
 
     // https://w3c.github.io/selection-api/#extensions-to-window-interface
     Selection? getSelection();