diff -r 8779ce81ea80 -r 4ee2af2194d4 mercurial/revset.py
--- a/mercurial/revset.py	Sun Aug 16 09:30:37 2015 +0900
+++ b/mercurial/revset.py	Thu Aug 20 17:19:56 2015 -0700
@@ -2967,6 +2967,8 @@
     """
     def __init__(self, data=()):
         if not isinstance(data, list):
+            if isinstance(data, set):
+                self._set = data
             data = list(data)
         self._list = data
         self._ascending = None