--- old/src/hotspot/share/gc/z/zHeap.inline.hpp	2019-05-29 11:25:13.503042326 +0200
+++ new/src/hotspot/share/gc/z/zHeap.inline.hpp	2019-05-29 11:25:13.316036453 +0200
@@ -135,7 +135,11 @@
 }
 
 inline bool ZHeap::is_oop(oop object) const {
-  return ZAddress::is_good(ZOop::to_address(object));
+  // Verify that we have a good address. Note that ZAddress::is_good()
+  // would not be a strong enough verification, since it only verifies
+  // that the metadata bits are good.
+  const uintptr_t addr = ZOop::to_address(object);
+  return ZAddress::good(addr) == addr;
 }
 
 #endif // SHARE_GC_Z_ZHEAP_INLINE_HPP