diff --git a/src/core/screen-private.h b/src/core/screen-private.h
index 3d02e1827..e3a3c7729 100644
--- a/src/core/screen-private.h
+++ b/src/core/screen-private.h
@@ -241,7 +241,7 @@ void     meta_screen_workspace_switched (MetaScreen         *screen,
 
 void meta_screen_set_active_workspace_hint (MetaScreen *screen);
 
-Window   meta_screen_create_guard_window (Display *xdisplay, MetaScreen *screen);
+void meta_screen_create_guard_window (MetaScreen *screen);
 
 gboolean meta_screen_handle_xevent (MetaScreen *screen,
                                     XEvent     *xevent);