--- old/src/share/vm/gc/g1/g1ConcurrentMark.inline.hpp	2016-09-13 11:46:27.945492008 +0200
+++ new/src/share/vm/gc/g1/g1ConcurrentMark.inline.hpp	2016-09-13 11:46:27.799487462 +0200
@@ -91,7 +91,9 @@
 
 #ifndef PRODUCT
 template<typename Fn>
-inline void G1CMMarkStack::iterate(Fn fn) {
+inline void G1CMMarkStack::iterate(Fn fn) const {
+  assert_at_safepoint(true);
+
   size_t num_chunks = 0;
 
   OopChunk* cur = _chunk_list;
@@ -102,7 +104,7 @@
       if (cur->data[i] == NULL) {
         break;
       }
-      fn((oop)cur->data[i]);
+      fn(cur->data[i]);
     }
     cur = cur->next;
     num_chunks++;