diff -r 850fdf70db2b -r 818a18cd69a8 src/share/vm/gc_implementation/shared/spaceDecorator.cpp
--- a/src/share/vm/gc_implementation/shared/spaceDecorator.cpp	Mon Jul 28 15:30:23 2008 -0700
+++ b/src/share/vm/gc_implementation/shared/spaceDecorator.cpp	Wed Jul 30 11:54:00 2008 -0700
@@ -39,7 +39,8 @@
 
 void SpaceMangler::set_top_for_allocations(HeapWord* v)  {
   if (v < end()) {
-    assert(is_mangled(v), "The high water mark is not mangled");
+    assert(!CheckZapUnusedHeapArea || is_mangled(v),
+      "The high water mark is not mangled");
   }
   _top_for_allocations = v;
 }