--- a/hgext/evolve.py	Mon Sep 10 16:54:58 2012 +0200
+++ b/hgext/evolve.py	Mon Sep 10 18:22:45 2012 +0200
@@ -1009,7 +1009,8 @@
         repo.ui.warn(_('whole rebase set is extinct and ignored.\n'))
         return {}
     root = min(rebaseset)
-    if not repo._rebasekeep and not repo[root].mutable():
+    if (not getattr(repo, '_rebasekeep', False)
+        and not repo[root].mutable()):
         raise util.Abort(_("can't rebase immutable changeset %s") % repo[root],
                          hint=_('see hg help phases for details'))
     return orig(repo, dest, rebaseset, *ags, **kws)