diff -r 1138e1d05207 -r c8f42c1926a5 mercurial/ui.py
--- a/mercurial/ui.py	Sat Oct 03 14:57:24 2015 +0900
+++ b/mercurial/ui.py	Sat Oct 03 23:10:40 2015 +0900
@@ -994,7 +994,7 @@
         """issue a developer warning message"""
         msg = 'devel-warn: ' + msg
         if self.tracebackflag:
-            util.debugstacktrace(msg, 2)
+            util.debugstacktrace(msg, 2, self.ferr, self.fout)
         else:
             curframe = inspect.currentframe()
             calframe = inspect.getouterframes(curframe, 2)