diff --git a/Tests/LibWeb/Text/expected/UIEvents/custom-mouse-event.txt b/Tests/LibWeb/Text/expected/UIEvents/custom-mouse-event.txt
new file mode 100644
index 0000000000..139787de3f
--- /dev/null
+++ b/Tests/LibWeb/Text/expected/UIEvents/custom-mouse-event.txt
@@ -0,0 +1,4 @@
+1. 10
+2. true
+3. true
+4. true
diff --git a/Tests/LibWeb/Text/input/UIEvents/custom-mouse-event.html b/Tests/LibWeb/Text/input/UIEvents/custom-mouse-event.html
new file mode 100644
index 0000000000..52962c867d
--- /dev/null
+++ b/Tests/LibWeb/Text/input/UIEvents/custom-mouse-event.html
@@ -0,0 +1,22 @@
+<script src="../include.js"></script>
+<script>
+    test(() => {
+        let testCounter = 1;
+        function testPart(part) {
+            println(`${testCounter}. ${JSON.stringify(part())}`);
+            testCounter++;
+        }
+
+        // 1. Creating a MouseEvent
+        testPart(() => new MouseEvent('click', { clientX: 10 }).clientX);
+
+        // 2. Creating a MouseEvent with modifier
+        testPart(() => new MouseEvent('click', { ctrlKey: true }).getModifierState('Control'));
+
+        // 3. Creating a MouseEvent with modifier
+        testPart(() => new MouseEvent('click', { modifierAltGraph: true }).getModifierState('AltGraph'));
+
+        // 4. Creating a MouseEvent with modifier
+        testPart(() => new MouseEvent('click', { modifierSymbolLock: true }).getModifierState('SymbolLock'));
+    });
+</script>
diff --git a/Userland/Libraries/LibWeb/UIEvents/MouseEvent.cpp b/Userland/Libraries/LibWeb/UIEvents/MouseEvent.cpp
index 79add6e12e..d796712579 100644
--- a/Userland/Libraries/LibWeb/UIEvents/MouseEvent.cpp
+++ b/Userland/Libraries/LibWeb/UIEvents/MouseEvent.cpp
@@ -113,6 +113,11 @@ JS::NonnullGCPtr<MouseEvent> MouseEvent::create(JS::Realm& realm, FlyString cons
     return realm.heap().allocate<MouseEvent>(realm, realm, event_name, event_init, page_x, page_y, offset_x, offset_y);
 }
 
+WebIDL::ExceptionOr<JS::NonnullGCPtr<MouseEvent>> MouseEvent::construct_impl(JS::Realm& realm, FlyString const& event_name, MouseEventInit const& event_init)
+{
+    return create(realm, event_name, event_init);
+}
+
 WebIDL::ExceptionOr<JS::NonnullGCPtr<MouseEvent>> MouseEvent::create_from_platform_event(JS::Realm& realm, FlyString const& event_name, CSSPixelPoint screen, CSSPixelPoint page, CSSPixelPoint client, CSSPixelPoint offset, Optional<CSSPixelPoint> movement, unsigned button, unsigned buttons, unsigned modifiers)
 {
     MouseEventInit event_init {};
diff --git a/Userland/Libraries/LibWeb/UIEvents/MouseEvent.h b/Userland/Libraries/LibWeb/UIEvents/MouseEvent.h
index 813e909ddf..a27d85ffe2 100644
--- a/Userland/Libraries/LibWeb/UIEvents/MouseEvent.h
+++ b/Userland/Libraries/LibWeb/UIEvents/MouseEvent.h
@@ -31,6 +31,7 @@ class MouseEvent : public UIEvent {
 public:
     [[nodiscard]] static JS::NonnullGCPtr<MouseEvent> create(JS::Realm&, FlyString const& event_name, MouseEventInit const& = {}, double page_x = 0, double page_y = 0, double offset_x = 0, double offset_y = 0);
     static WebIDL::ExceptionOr<JS::NonnullGCPtr<MouseEvent>> create_from_platform_event(JS::Realm&, FlyString const& event_name, CSSPixelPoint screen, CSSPixelPoint page, CSSPixelPoint client, CSSPixelPoint offset, Optional<CSSPixelPoint> movement, unsigned button, unsigned buttons, unsigned modifiers);
+    static WebIDL::ExceptionOr<JS::NonnullGCPtr<MouseEvent>> construct_impl(JS::Realm&, FlyString const& event_name, MouseEventInit const&);
 
     virtual ~MouseEvent() override;
 
diff --git a/Userland/Libraries/LibWeb/UIEvents/MouseEvent.idl b/Userland/Libraries/LibWeb/UIEvents/MouseEvent.idl
index 31c4af90ce..7134d33244 100644
--- a/Userland/Libraries/LibWeb/UIEvents/MouseEvent.idl
+++ b/Userland/Libraries/LibWeb/UIEvents/MouseEvent.idl
@@ -3,7 +3,7 @@
 // https://w3c.github.io/uievents/#mouseevent
 [Exposed=Window]
 interface MouseEvent : UIEvent {
-    // FIXME: constructor(DOMString type, optional MouseEventInit eventInitDict = {});
+    constructor(DOMString type, optional MouseEventInit eventInitDict = {});
 
     // https://drafts.csswg.org/cssom-view/#extensions-to-the-mouseevent-interface
     readonly attribute double screenX;