--- a/src/hotspot/share/oops/klassVtable.cpp	Fri Aug 31 12:41:00 2018 +0200
+++ b/src/hotspot/share/oops/klassVtable.cpp	Fri Aug 31 07:03:46 2018 -0400
@@ -1595,7 +1595,8 @@
   }
 
   static void compute() {
-    ClassLoaderDataGraph::classes_do(do_class);
+    LockedClassesDo locked_do_class(&do_class);
+    ClassLoaderDataGraph::classes_do(&locked_do_class);
     fixed  = no_klasses * oopSize;      // vtable length
     // filler size is a conservative approximation
     filler = oopSize * (no_klasses - no_instance_klasses) * (sizeof(InstanceKlass) - sizeof(ArrayKlass) - 1);