diff --git a/gtk/gtktooltip.c b/gtk/gtktooltip.c
index fa4c8b68cd..fd2ba1413b 100644
--- a/gtk/gtktooltip.c
+++ b/gtk/gtktooltip.c
@@ -904,7 +904,7 @@ gtk_tooltip_set_last_window (GtkTooltip *tooltip,
 
   tooltip->last_window = window;
 
-  if (window)
+  if (tooltip->last_window)
     g_object_add_weak_pointer (G_OBJECT (tooltip->last_window),
 			       (gpointer *) &tooltip->last_window);