--- old/src/hotspot/share/gc/g1/g1HeapVerifier.cpp	2019-03-13 14:03:06.568178375 +0100
+++ new/src/hotspot/share/gc/g1/g1HeapVerifier.cpp	2019-03-13 14:03:06.356172617 +0100
@@ -371,6 +371,7 @@
   }
 
   bool do_heap_region(HeapRegion* r) {
+    guarantee(!r->has_index_in_opt_cset(), "Region %u still has opt collection set index %u", r->hrm_index(), r->index_in_opt_cset());
     guarantee(!r->is_young() || r->rem_set()->is_complete(), "Remembered set for Young region %u must be complete, is %s", r->hrm_index(), r->rem_set()->get_state_str());
     // Humongous and old regions regions might be of any state, so can't check here.
     guarantee(!r->is_free() || !r->rem_set()->is_tracked(), "Remembered set for free region %u must be untracked, is %s", r->hrm_index(), r->rem_set()->get_state_str());