--- a/mercurial/revlog.py	Sat Dec 05 22:19:48 2015 -0500
+++ b/mercurial/revlog.py	Fri Dec 04 17:22:26 2015 -0800
@@ -1406,7 +1406,6 @@
         curr = len(self)
         prev = curr - 1
         base = chainbase = curr
-        chainlen = None
         offset = self.end(prev)
         delta = None
         if self._basecache is None: