--- a/hgext/mq.py	Sat Mar 03 09:50:07 2018 -0500
+++ b/hgext/mq.py	Sat Mar 03 21:01:07 2018 +0530
@@ -723,7 +723,8 @@
         try:
             os.unlink(undo)
         except OSError as inst:
-            self.ui.warn(_('error removing undo: %s\n') % str(inst))
+            self.ui.warn(_('error removing undo: %s\n') %
+                         util.forcebytestr(inst))
 
     def backup(self, repo, files, copy=False):
         # backup local changes in --force case