--- old/src/hotspot/share/gc/z/zWorkers.hpp	2019-11-28 15:24:33.806415580 +0100
+++ new/src/hotspot/share/gc/z/zWorkers.hpp	2019-11-28 15:24:33.539406495 +0100
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2015, 2018, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2015, 2019, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -27,6 +27,7 @@
 #include "gc/shared/workgroup.hpp"
 #include "memory/allocation.hpp"
 
+class ThreadClosure;
 class ZTask;
 
 class ZWorkers {