--- old/src/share/vm/runtime/objectMonitor.inline.hpp	2015-10-08 22:16:03.655922159 +0200
+++ new/src/share/vm/runtime/objectMonitor.inline.hpp	2015-10-08 22:16:03.560924428 +0200
@@ -75,6 +75,9 @@
 
 inline void ObjectMonitor::set_object(void* obj) {
   _object = obj;
+  if (_object != (cast_to_oop<intptr_t>(-1))) {
+    assert(oop(_object) == oopDesc::bs()->write_barrier(oop(_object)), "expect to-space copy");
+  }
 }
 
 inline bool ObjectMonitor::check(TRAPS) {