diff -up metacity-2.20.0/src/menu.c.single-workspace-crash metacity-2.20.0/src/menu.c
--- metacity-2.20.0/src/menu.c.single-workspace-crash	2007-11-11 23:41:43.000000000 -0500
+++ metacity-2.20.0/src/menu.c	2007-11-11 23:41:52.000000000 -0500
@@ -474,10 +474,12 @@ meta_window_menu_new   (MetaFrames      
                                        g_free, FALSE, FALSE);
             }
 
-
-          gtk_menu_shell_append (GTK_MENU_SHELL (menu->menu), mi);
+          if (mi)
+            {
+              gtk_menu_shell_append (GTK_MENU_SHELL (menu->menu), mi);
           
-          gtk_widget_show (mi);
+              gtk_widget_show (mi);
+            }
         }
     }