Index: window.c
===================================================================
--- window.c	(revision 48652)
+++ window.c	(working copy)
@@ -2185,7 +2185,7 @@
        /* If the window was created, the class will be dereferenced by co_UserDestroyWindow */
        if (Window) 
             co_UserDestroyWindow(Window);
-       else
+       else if (Class)
            IntDereferenceClass(Class, pti->pDeskInfo, pti->ppi);
    }