--- a/src/hotspot/share/runtime/mutex.cpp	Mon Oct 29 08:38:59 2018 -0400
+++ b/src/hotspot/share/runtime/mutex.cpp	Mon Oct 29 10:21:34 2018 -0400
@@ -876,7 +876,7 @@
 #endif // CHECK_UNHANDLED_OOPS
 
   debug_only(check_prelock_state(Self, StrictSafepointChecks));
-  assert(_owner != Self, "invariant");
+  assert(_owner != Self, "this lock %s is already held by this thread", name());
   assert(_OnDeck != Self->_MutexEvent, "invariant");
 
   if (TryFast()) {