--- a/src/hotspot/share/ci/ciInstanceKlass.cpp	Fri Aug 10 22:38:18 2018 -0400
+++ b/src/hotspot/share/ci/ciInstanceKlass.cpp	Sat Aug 11 12:49:33 2018 -0400
@@ -596,6 +596,7 @@
     // Go into the VM to fetch the implementor.
     {
       VM_ENTRY_MARK;
+      MutexLocker ml(Compile_lock);
       Klass* k = get_instanceKlass()->implementor();
       if (k != NULL) {
         if (k == get_instanceKlass()) {