--- old/src/hotspot/share/gc/z/zRelocationSet.inline.hpp	2019-12-15 23:51:32.948844462 +0100
+++ new/src/hotspot/share/gc/z/zRelocationSet.inline.hpp	2019-12-15 23:51:32.700840393 +0100
@@ -38,7 +38,7 @@
 
   if (parallel) {
     if (_next < nforwardings) {
-      const size_t next = Atomic::add(&_next, 1u) - 1u;
+      const size_t next = Atomic::fetch_and_add(&_next, 1u);
       if (next < nforwardings) {
         *forwarding = _relocation_set->_forwardings[next];
         return true;