--- old/src/share/vm/gc/shenandoah/vm_operations_shenandoah.cpp	2017-10-05 21:08:08.636161414 +0200
+++ new/src/share/vm/gc/shenandoah/vm_operations_shenandoah.cpp	2017-10-05 21:08:08.528161151 +0200
@@ -48,7 +48,9 @@
 
   ShenandoahWorkerScope scope(workers, nworkers);
 
-  assert(sh->is_next_bitmap_clear(), "need clear marking bitmap");
+  assert(sh->is_bitmap_clear(), "need clear marking bitmap");
+
+  sh->set_bitmap_valid(false);
 
   sh->start_concurrent_marking();
 }
@@ -86,6 +88,7 @@
   if (! sh->cancelled_concgc()) {
     GCTraceTime(Info, gc) time("Pause Final Mark", sh->gc_timer(), GCCause::_no_gc, true);
     sh->concurrentMark()->finish_mark_from_roots();
+    sh->set_bitmap_valid(true);
     sh->stop_concurrent_marking();
 
     {