diff -r b970418bbafe -r b68c9d232db6 mercurial/revset.py
--- a/mercurial/revset.py	Tue Aug 18 16:40:10 2015 -0400
+++ b/mercurial/revset.py	Fri Aug 14 15:43:29 2015 +0900
@@ -94,6 +94,7 @@
     if not roots:
         return baseset()
     parentrevs = repo.changelog.parentrevs
+    roots = set(roots)
     visit = list(heads)
     reachable = set()
     seen = {}
@@ -133,7 +134,7 @@
     # XXX this should be 'parentset.min()' assuming 'parentset' is a smartset
     # (and if it is not, it should.)
     minroot = min(roots)
-    roots = set(roots)
+    roots = list(roots)
     heads = list(heads)
     try:
         return repo.changelog.reachableroots(minroot, heads, roots, includepath)