diff -r 4612cded5176 -r ea52a2d4f42c mercurial/revlog.py
--- a/mercurial/revlog.py	Mon Feb 08 15:36:34 2010 +0100
+++ b/mercurial/revlog.py	Mon Feb 08 17:28:19 2010 +0100
@@ -343,6 +343,8 @@
         return index, nodemap, None
 
     def packentry(self, entry, node, version, rev):
+        if gettype(entry[0]):
+            raise RevlogError(_("index entry flags need RevlogNG"))
         e2 = (getoffset(entry[0]), entry[1], entry[3], entry[4],
               node(entry[5]), node(entry[6]), entry[7])
         return _pack(indexformatv0, *e2)