diff --git a/src/os_unix.c b/src/os_unix.c
index 150bdad..9fcebd6 100644
--- a/src/os_unix.c
+++ b/src/os_unix.c
@@ -1738,6 +1738,11 @@
     }
     if (x11_window == 0 || x11_display == NULL)
 	return (result = FAIL);
+
+# ifdef FEAT_EVAL
+    set_vim_var_nr(VV_WINDOWID, (long)x11_window);
+# endif
+
     return (result = OK);
 }