diff --git a/src/ui/ui.c b/src/ui/ui.c
index 963be7c1a..438188072 100644
--- a/src/ui/ui.c
+++ b/src/ui/ui.c
@@ -653,3 +653,11 @@ meta_ui_window_is_widget (MetaUI *ui,
   else
     return FALSE;
 }
+
+gboolean
+meta_ui_window_is_dummy (MetaUI *ui,
+                         Window  xwindow)
+{
+  GdkWindow *frames_window = gtk_widget_get_window (GTK_WIDGET (ui->frames));
+  return xwindow == gdk_x11_window_get_xid (frames_window);
+}
diff --git a/src/ui/ui.h b/src/ui/ui.h
index 2dfeead9a..600338986 100644
--- a/src/ui/ui.h
+++ b/src/ui/ui.h
@@ -116,5 +116,7 @@ gboolean meta_ui_have_a_theme      (void);
 
 gboolean meta_ui_window_is_widget (MetaUI *ui,
                                    Window  xwindow);
+gboolean meta_ui_window_is_dummy  (MetaUI *ui,
+                                   Window  xwindow);
 
 #endif