diff --git a/plugins/task-button.c b/plugins/task-button.c
index ea8ca9c..46cc5f7 100644
--- a/plugins/task-button.c
+++ b/plugins/task-button.c
@@ -1660,6 +1660,9 @@ gboolean task_button_window_focus_changed(TaskButton *button, Window *win)
     TaskDetails *details;
     gboolean res = FALSE;
 
+    if (!win)
+	    return res;
+
     g_return_val_if_fail(PANEL_IS_TASK_BUTTON(button), FALSE);
 
     for (l = button->details; l; l = l->next)