diff -r 4584eec9aead -r e02b16f496f2 mercurial/revset.py
--- a/mercurial/revset.py	Fri Oct 10 14:22:23 2014 -0700
+++ b/mercurial/revset.py	Fri Oct 10 14:27:05 2014 -0700
@@ -2064,7 +2064,7 @@
         tree = findaliases(ui, tree)
     weight, tree = optimize(tree, True)
     def mfunc(repo, subset):
-        if util.safehasattr(subset, 'set'):
+        if util.safehasattr(subset, 'isascending'):
             result = getset(repo, subset, tree)
         else:
             result = getset(repo, baseset(subset), tree)