diff -r 44dc3d796110 -r 3aba4a42d8ad src/hotspot/share/gc/z/zHeapIterator.cpp
--- a/src/hotspot/share/gc/z/zHeapIterator.cpp	Mon Oct 28 11:21:23 2019 +0100
+++ b/src/hotspot/share/gc/z/zHeapIterator.cpp	Mon Oct 28 11:23:28 2019 +0100
@@ -24,6 +24,7 @@
 #include "precompiled.hpp"
 #include "classfile/classLoaderData.hpp"
 #include "classfile/classLoaderDataGraph.hpp"
+#include "gc/z/zAddress.inline.hpp"
 #include "gc/z/zBarrier.inline.hpp"
 #include "gc/z/zGlobals.hpp"
 #include "gc/z/zGranuleMap.inline.hpp"
@@ -148,11 +149,11 @@
 }
 
 ZHeapIteratorBitMap* ZHeapIterator::object_map(oop obj) {
-  const uintptr_t addr = ZOop::to_address(obj);
-  ZHeapIteratorBitMap* map = _visit_map.get(addr);
+  const uintptr_t offset = ZAddress::offset(ZOop::to_address(obj));
+  ZHeapIteratorBitMap* map = _visit_map.get(offset);
   if (map == NULL) {
     map = new ZHeapIteratorBitMap(object_index_max());
-    _visit_map.put(addr, map);
+    _visit_map.put(offset, map);
   }
 
   return map;