diff --git a/Libraries/LibGUI/Forward.h b/Libraries/LibGUI/Forward.h
index 5c39ae4a3f7..610e211dd65 100644
--- a/Libraries/LibGUI/Forward.h
+++ b/Libraries/LibGUI/Forward.h
@@ -89,6 +89,7 @@ class VerticalBoxLayout;
 class VerticalSlider;
 class WMEvent;
 class Widget;
+class WidgetClassRegistration;
 class Window;
 class WindowServerConnection;