--- old/src/hotspot/share/gc/g1/g1ConcurrentMark.hpp	2018-04-27 15:29:44.882202879 +0200
+++ new/src/hotspot/share/gc/g1/g1ConcurrentMark.hpp	2018-04-27 15:29:44.638202888 +0200
@@ -36,6 +36,7 @@
 class ConcurrentGCTimer;
 class G1ConcurrentMarkThread;
 class G1CollectedHeap;
+class G1CMOopClosure;
 class G1CMTask;
 class G1ConcurrentMark;
 class G1OldTracer;