diff -r b5a5f30c483d -r 6071e0581859 src/share/vm/gc_implementation/g1/heapRegion.hpp
--- a/src/share/vm/gc_implementation/g1/heapRegion.hpp	Mon Nov 21 09:24:56 2011 -0800
+++ b/src/share/vm/gc_implementation/g1/heapRegion.hpp	Fri Nov 18 12:27:10 2011 -0800
@@ -416,7 +416,7 @@
 
   void add_to_marked_bytes(size_t incr_bytes) {
     _next_marked_bytes = _next_marked_bytes + incr_bytes;
-    guarantee( _next_marked_bytes <= used(), "invariant" );
+    assert(_next_marked_bytes <= used(), "invariant" );
   }
 
   void zero_marked_bytes()      {