diff -r 974389427e5f -r e994b034e91e mercurial/obsolete.py
--- a/mercurial/obsolete.py	Thu Oct 09 00:10:10 2014 -0700
+++ b/mercurial/obsolete.py	Tue Sep 16 17:52:40 2014 -0700
@@ -450,7 +450,7 @@
     # parents: (tuple of nodeid) or None, parents of precursors
     #          None is used when no data has been recorded
 
-    def __init__(self, sopener):
+    def __init__(self, sopener, defaultformat=_fm0version):
         # caches for various obsolescence related cache
         self.caches = {}
         self._all = []
@@ -459,7 +459,7 @@
         self.children = {}
         self.sopener = sopener
         data = sopener.tryread('obsstore')
-        self._version = _fm0version
+        self._version = defaultformat
         if data:
             self._version, markers = _readmarkers(data)
             self._load(markers)