diff --git a/src/core/window.c b/src/core/window.c
index 47c29d94a8..5ac054e88f 100644
--- a/src/core/window.c
+++ b/src/core/window.c
@@ -5993,6 +5993,9 @@ meta_window_foreach_transient (MetaWindow            *window,
   GSList *windows;
   GSList *tmp;
 
+  if (!window)
+    return;
+
   windows = meta_display_list_windows (window->display, META_LIST_DEFAULT);
 
   tmp = windows;