--- a/layout/tables/nsCellMap.cpp
+++ b/layout/tables/nsCellMap.cpp
@@ -319,17 +319,17 @@ nsTableCellMap::Synchronize(nsTableFrame
   // XXXbz this fails if orderedRowGroups is missing some row groups
   // (due to OOM when appending to the array, e.g. -- we leak maps in
   // that case).
   
   // Scope |map| outside the loop so we can use it as a hint.
   nsCellMap* map = nsnull;
   for (PRUint32 rgX = 0; rgX < orderedRowGroups.Length(); rgX++) {
     nsTableRowGroupFrame* rgFrame = orderedRowGroups[rgX];
-    map = GetMapFor(rgFrame, map);
+    map = GetMapFor((nsTableRowGroupFrame*)rgFrame->GetFirstInFlow(), map);
     if (map) {
       if (!maps.AppendElement(map)) {
         delete map;
         NS_WARNING("Could not AppendElement");
       }
     }
   }