--- old/src/hotspot/share/gc/g1/g1ParScanThreadState.inline.hpp	2018-10-16 14:29:31.212306370 +0200
+++ new/src/hotspot/share/gc/g1/g1ParScanThreadState.inline.hpp	2018-10-16 14:29:30.796293632 +0200
@@ -25,6 +25,7 @@
 #ifndef SHARE_VM_GC_G1_G1PARSCANTHREADSTATE_INLINE_HPP
 #define SHARE_VM_GC_G1_G1PARSCANTHREADSTATE_INLINE_HPP
 
+#include "gc/g1/g1CollectedHeap.inline.hpp"
 #include "gc/g1/g1ParScanThreadState.hpp"
 #include "gc/g1/g1RemSet.hpp"
 #include "oops/access.inline.hpp"
@@ -40,6 +41,12 @@
   // processed multiple times, and so we might get references into old gen here.
   // So we need to redo this check.
   const InCSetState in_cset_state = _g1h->in_cset_state(obj);
+  // References pushed onto the work stack should never point to a humongous region
+  // as they are not added to the collection set due to above precondition.
+  assert(!in_cset_state.is_humongous(),
+         "Obj " PTR_FORMAT " should not refer to humongous region %u from " PTR_FORMAT,
+         p2i(obj), _g1h->addr_to_region((HeapWord*)obj), p2i(p));
+
   if (!in_cset_state.is_in_cset()) {
     // In this case somebody else already did all the work.
     return;