diff -r 1fad808f2a6b -r afef1e362d65 mercurial/commands.py
--- a/mercurial/commands.py	Sun Jul 08 17:37:05 2018 +0900
+++ b/mercurial/commands.py	Sun Jul 08 17:45:42 2018 +0900
@@ -1220,7 +1220,7 @@
         other = hg.peer(repo, opts, dest)
         revs = [repo[r].hex() for r in revs]
         revs, checkout = hg.addbranchrevs(repo, repo, branches, revs)
-        heads = revs and map(repo.lookup, revs) or revs
+        heads = revs and pycompat.maplist(repo.lookup, revs) or revs
         outgoing = discovery.findcommonoutgoing(repo, other,
                                                 onlyheads=heads,
                                                 force=opts.get('force'),