diff --git a/lisp/ChangeLog b/lisp/ChangeLog
index d58ced9fbe4..3e5c73ebd2b 100644
--- a/lisp/ChangeLog
+++ b/lisp/ChangeLog
@@ -1,3 +1,9 @@
+2005-11-03  Sam Steingold  <sds@gnu.org>
+
+	* mwheel.el (mouse-wheel-down-event, mouse-wheel-up-event): Use
+	system-type instead of window-system because window-system is not
+	correctly defined during loadup.
+
 2005-11-02  Mark A. Hershberger  <mah@everybody.org>
 
 	* xml.el (xml-syntax-table): Allow xml.el to compile in xemacs.
diff --git a/lisp/mwheel.el b/lisp/mwheel.el
index 391ce3a5e04..c4e604bfd6e 100644
--- a/lisp/mwheel.el
+++ b/lisp/mwheel.el
@@ -59,7 +59,7 @@
                         'mouse-wheel-down-event)
 (defcustom mouse-wheel-down-event
   ;; In the latest versions of XEmacs, we could just use mouse-%s as well.
-  (if (memq window-system '(w32 mac))
+  (if (memq system-type '(windows-nt macos))
       'wheel-up
     (intern (format (if (featurep 'xemacs) "button%s" "mouse-%s")
 		    mouse-wheel-down-button)))
@@ -73,7 +73,7 @@
                         'mouse-wheel-up-event)
 (defcustom mouse-wheel-up-event
   ;; In the latest versions of XEmacs, we could just use mouse-%s as well.
-  (if (memq window-system '(w32 mac))
+  (if (memq system-type '(windows-nt macos))
       'wheel-down
     (intern (format (if (featurep 'xemacs) "button%s" "mouse-%s")
 		    mouse-wheel-up-button)))