diff -r 46e1a4e24225 -r 612db9d7e76a mercurial/bookmarks.py
--- a/mercurial/bookmarks.py	Fri Oct 19 00:30:11 2012 +0200
+++ b/mercurial/bookmarks.py	Tue Oct 16 15:49:58 2012 +0200
@@ -267,7 +267,7 @@
                 if c.phase() > phases.public:
                     # obsolescence marker does not apply to public changeset
                     succs.update(obsolete.allsuccessors(repo.obsstore,
-                                                        c.node()))
+                                                        [c.node()]))
             validdests = set(repo.set('%ln::', succs))
         validdests.remove(old)
         return new in validdests