--- old/src/hotspot/share/gc/shenandoah/shenandoahTraversalGC.cpp	2020-04-22 11:59:06.308926426 +0200
+++ new/src/hotspot/share/gc/shenandoah/shenandoahTraversalGC.cpp	2020-04-22 11:59:06.112926360 +0200
@@ -314,6 +314,7 @@
   ShenandoahMarkingContext* const ctx = _heap->marking_context();
   for (size_t i = 0; i < num_regions; i++) {
     ShenandoahHeapRegion* region = _heap->get_region(i);
+    region->set_update_watermark(region->top());
     if (_heap->is_bitmap_slice_committed(region)) {
       if (_traversal_set.is_in(i)) {
         ctx->capture_top_at_mark_start(region);