Index: linux-2.6.18-mm2/include/linux/mm.h
===================================================================
--- linux-2.6.18-mm2.orig/include/linux/mm.h	2006-09-30 13:22:27.732989275 -0500
+++ linux-2.6.18-mm2/include/linux/mm.h	2006-09-30 13:23:06.604463587 -0500
@@ -447,6 +447,7 @@ static inline enum zone_type page_zonenu
  */
 static inline int page_zone_id(struct page *page)
 {
+	BUG_ON(ZONEID_PGSHIFT == 0 && ZONEID_MASK);
 	return (page->flags >> ZONEID_PGSHIFT) & ZONEID_MASK;
 }