--- a/src/share/vm/gc_implementation/g1/heapRegion.hpp	Fri Oct 21 07:24:06 2011 -0400
+++ b/src/share/vm/gc_implementation/g1/heapRegion.hpp	Fri Oct 21 12:42:42 2011 -0400
@@ -431,6 +431,14 @@
     return _humongous_start_region;
   }
 
+  // Same as Space::is_in_reserved, but will use the original size of the region.
+  // The original size is different only for start humongous regions. They get
+  // their _end set up to be the end of the last continues region of the
+  // corresponding humongous object.
+  bool is_in_reserved_raw(const void* p) const {
+    return _bottom <= p && p < _orig_end;
+  }
+
   // Makes the current region be a "starts humongous" region, i.e.,
   // the first region in a series of one or more contiguous regions
   // that will contain a single "humongous" object. The two parameters

--- a/src/share/vm/gc_implementation/g1/heapRegionRemSet.cpp	Fri Oct 21 07:24:06 2011 -0400
+++ b/src/share/vm/gc_implementation/g1/heapRegionRemSet.cpp	Fri Oct 21 12:42:42 2011 -0400
@@ -143,7 +143,11 @@
     // If the test below fails, then this table was reused concurrently
     // with this operation.  This is OK, since the old table was coarsened,
     // and adding a bit to the new table is never incorrect.
-    if (loc_hr->is_in_reserved(from)) {
+    // If the table used to belong to a continues humongous region and is
+    // now reused for the corresponding start humongous region, we need to
+    // make sure that we detect this. Thus, we call is_in_reserved_raw()
+    // instead of just is_in_reserved() here.
+    if (loc_hr->is_in_reserved_raw(from)) {
       size_t hw_offset = pointer_delta((HeapWord*)from, loc_hr->bottom());
       CardIdx_t from_card = (CardIdx_t)
           hw_offset >> (CardTableModRefBS::card_shift - LogHeapWordSize);