diff -r 277f4fe6d01a -r 39d13b8c101d mercurial/ui.py
--- a/mercurial/ui.py	Thu Oct 20 23:40:24 2016 +0900
+++ b/mercurial/ui.py	Thu Oct 20 23:53:36 2016 +0900
@@ -130,9 +130,9 @@
 
             self.httppasswordmgrdb = src.httppasswordmgrdb
         else:
-            self.fout = sys.stdout
-            self.ferr = sys.stderr
-            self.fin = sys.stdin
+            self.fout = util.stdout
+            self.ferr = util.stderr
+            self.fin = util.stdin
 
             # shared read-only environment
             self.environ = os.environ