diff -r bb18957ad21e -r df6caf649ff7 src/share/vm/gc_implementation/g1/satbQueue.cpp
--- a/src/share/vm/gc_implementation/g1/satbQueue.cpp	Fri Jul 10 16:01:20 2009 -0700
+++ b/src/share/vm/gc_implementation/g1/satbQueue.cpp	Tue Jul 14 15:40:39 2009 -0700
@@ -43,6 +43,18 @@
     }
   }
 }
+
+#ifdef ASSERT
+void ObjPtrQueue::verify_oops_in_buffer() {
+  if (_buf == NULL) return;
+  for (size_t i = _index; i < _sz; i += oopSize) {
+    oop obj = (oop)_buf[byte_index_to_index((int)i)];
+    assert(obj != NULL && obj->is_oop(true /* ignore mark word */),
+           "Not an oop");
+  }
+}
+#endif
+
 #ifdef _MSC_VER // the use of 'this' below gets a warning, make it go away
 #pragma warning( disable:4355 ) // 'this' : used in base member initializer list
 #endif // _MSC_VER
@@ -66,6 +78,7 @@
 
 
 void SATBMarkQueueSet::handle_zero_index_for_thread(JavaThread* t) {
+  DEBUG_ONLY(t->satb_mark_queue().verify_oops_in_buffer();)
   t->satb_mark_queue().handle_zero_index();
 }
 
@@ -143,7 +156,7 @@
     }
     _completed_buffers_tail = NULL;
     _n_completed_buffers = 0;
-    debug_only(assert_completed_buffer_list_len_correct_locked());
+    DEBUG_ONLY(assert_completed_buffer_list_len_correct_locked());
   }
   while (buffers_to_delete != NULL) {
     CompletedBufferNode* nd = buffers_to_delete;