diff -r 2959c3e986e0 -r bd872f64a8ba mercurial/cmdutil.py
--- a/mercurial/cmdutil.py	Sat May 06 04:51:25 2017 +0530
+++ b/mercurial/cmdutil.py	Fri Feb 10 16:56:29 2017 -0800
@@ -1693,7 +1693,7 @@
             last = filelog.rev(node)
 
         # keep track of all ancestors of the file
-        ancestors = set([filelog.linkrev(last)])
+        ancestors = {filelog.linkrev(last)}
 
         # iterate from latest to oldest revision
         for rev, flparentlinkrevs, copied in filerevgen(filelog, last):