--- a/mercurial/context.py	Mon Apr 15 01:59:11 2013 +0200
+++ b/mercurial/context.py	Tue Apr 16 10:08:18 2013 -0700
@@ -756,7 +756,7 @@
             return pl
 
         a, b = (self._path, self._filenode), (fc2._path, fc2._filenode)
-        v = ancestor.ancestor(a, b, parents)
+        v = ancestor.genericancestor(a, b, parents)
         if v:
             f, n = v
             return filectx(self._repo, f, fileid=n, filelog=flcache[f])