diff --git a/mitterlib/ui/ui_pygtk.py b/mitterlib/ui/ui_pygtk.py
index 0970bdb..2905bab 100644
--- a/mitterlib/ui/ui_pygtk.py
+++ b/mitterlib/ui/ui_pygtk.py
@@ -1292,8 +1292,11 @@ class Interface(object):
         self.update_text.set_sensitive(False)
         self.statusbar.push(self.statusbar_context, 'Updating your status...')
 
-    def quit_app(self, widget=None):
+    def quit_app(self, widget=None, user_data=None):
+        """Callback when the window is destroyed or the user selects
+        "Quit"."""
         gtk.main_quit()
+        return
 
     # ------------------------------------------------------------
     # Required functions for all interfaces