diff --git a/src/gui_w32.c b/src/gui_w32.c
index cdb1abb..128869e 100644
--- a/src/gui_w32.c
+++ b/src/gui_w32.c
@@ -1575,7 +1575,7 @@
 
 #ifdef FEAT_EVAL
     /* set the v:windowid variable */
-    set_vim_var_nr(VV_WINDOWID, (long)s_hwnd);
+    set_vim_var_nr(VV_WINDOWID, HandleToLong(s_hwnd));
 #endif
 
 theend: