--- old/src/share/vm/gc_implementation/g1/concurrentMark.cpp	2014-07-14 09:54:08.853583224 +0200
+++ new/src/share/vm/gc_implementation/g1/concurrentMark.cpp	2014-07-14 09:54:08.768580739 +0200
@@ -891,6 +891,10 @@
   guarantee(!g1h->mark_in_progress(), "invariant");
 }
 
+bool ConcurrentMark::nextMarkBitmapIsClear() {
+  return _nextMarkBitMap->getNextMarkedWordAddress(_heap_start, _heap_end) == _heap_end;
+}
+
 class NoteStartOfMarkHRClosure: public HeapRegionClosure {
 public:
   bool doHeapRegion(HeapRegion* r) {
--- old/src/share/vm/gc_implementation/g1/concurrentMark.hpp	2014-07-14 09:54:09.477601466 +0200
+++ new/src/share/vm/gc_implementation/g1/concurrentMark.hpp	2014-07-14 09:54:09.394599039 +0200
@@ -736,6 +736,9 @@
   // Clear the next marking bitmap (will be called concurrently).
   void clearNextBitmap();
 
+  // Return whether the next mark bitmap has no marks set.
+  bool nextMarkBitmapIsClear();
+
   // These two do the work that needs to be done before and after the
   // initial root checkpoint. Since this checkpoint can be done at two
   // different points (i.e. an explicit pause or piggy-backed on a
--- old/src/share/vm/gc_implementation/g1/concurrentMarkThread.cpp	2014-07-14 09:54:10.027617544 +0200
+++ new/src/share/vm/gc_implementation/g1/concurrentMarkThread.cpp	2014-07-14 09:54:09.946615176 +0200
@@ -283,7 +283,7 @@
         SuspendibleThreadSetJoiner sts;
         _cm->clearNextBitmap();
       } else {
-        g1h->check_bitmaps("Reset bitmaps");
+        assert(!G1VerifyBitmaps || _cm->nextMarkBitmapIsClear(), "Next mark bitmap must be clear");
       }
     }