diff -r 2959c3e986e0 -r bd872f64a8ba mercurial/wireproto.py
--- a/mercurial/wireproto.py	Sat May 06 04:51:25 2017 +0530
+++ b/mercurial/wireproto.py	Fri Feb 10 16:56:29 2017 -0800
@@ -759,7 +759,7 @@
             caps.append('stream-preferred')
         requiredformats = repo.requirements & repo.supportedformats
         # if our local revlogs are just revlogv1, add 'stream' cap
-        if not requiredformats - set(('revlogv1',)):
+        if not requiredformats - {'revlogv1'}:
             caps.append('stream')
         # otherwise, add 'streamreqs' detailing our local revlog format
         else: