--- a/hgext/obsolete.py	Mon Sep 19 01:11:10 2011 +0200
+++ b/hgext/obsolete.py	Mon Sep 19 01:55:35 2011 +0200
@@ -350,7 +350,10 @@
             f = self.opener('obsolete-relations', 'w', atomictemp=True)
             try:
                 _obsserialise(self._obssubrels, f)
-                f.rename()
+                try:
+                    f.rename()
+                except AttributeError: # old version
+                    f.close()
             finally:
                 f.close()