--- old/src/share/vm/gc/g1/heapRegion.inline.hpp	2015-11-03 17:15:25.908161491 +0100
+++ new/src/share/vm/gc/g1/heapRegion.inline.hpp	2015-11-03 17:15:25.808160995 +0100
@@ -118,6 +118,12 @@
 
   if (!this->is_in(p)) {
     HeapRegion* hr = g1h->heap_region_containing(p);
+#ifdef ASSERT
+    assert(hr->is_humongous(), "This case can only happen for humongous regions");
+    oop obj = oop(hr->humongous_start_region()->bottom());
+    assert((HeapWord*)obj <= p, "p must be in humongous object");
+    assert(p <= (HeapWord*)obj + obj->size(), "p must be in humongous object");
+#endif
     return hr->block_is_obj(p);
   }
   if (ClassUnloadingWithConcurrentMark) {