--- a/mercurial/hg.py	Wed Jun 08 13:44:41 2011 -0500
+++ b/mercurial/hg.py	Mon Jun 06 21:18:35 2011 +0200
@@ -318,7 +318,7 @@
 
             revs = None
             if rev:
-                if 'lookup' not in srcrepo.capabilities:
+                if not srcrepo.capable('lookup'):
                     raise util.Abort(_("src repository does not support "
                                        "revision lookup and so doesn't "
                                        "support clone by revision"))