--- old/src/hotspot/share/oops/valueKlass.cpp	2018-05-21 11:52:12.524070857 +0200
+++ new/src/hotspot/share/oops/valueKlass.cpp	2018-05-21 11:52:12.212065299 +0200
@@ -93,7 +93,9 @@
 instanceOop ValueKlass::allocate_instance(TRAPS) {
   int size = size_helper();  // Query before forming handle.
 
-  return (instanceOop)CollectedHeap::obj_allocate(this, size, CHECK_NULL);
+  instanceOop oop = (instanceOop)CollectedHeap::obj_allocate(this, size, CHECK_NULL);
+  assert(oop->mark()->is_always_locked(), "Unlocked value type");
+  return oop;
 }
 
 instanceOop ValueKlass::allocate_buffered_or_heap_instance(bool* in_heap, TRAPS) {
@@ -618,3 +620,13 @@
     }
   }
 }
+
+void ValueKlass::verify_on(outputStream* st) {
+  InstanceKlass::verify_on(st);
+  guarantee(prototype_header()->is_always_locked(), "Prototype header is not always locked");
+}
+
+void ValueKlass::oop_verify_on(oop obj, outputStream* st) {
+  InstanceKlass::oop_verify_on(obj, st);
+  guarantee(obj->mark()->is_always_locked(), "Header is not always locked");
+}