diff -r ffd574c144d2 -r 691c68bc1222 mercurial/ui.py
--- a/mercurial/ui.py	Sun Nov 11 19:35:33 2018 +0900
+++ b/mercurial/ui.py	Sun Nov 11 19:36:21 2018 +0900
@@ -1742,6 +1742,7 @@
         if not activeloggers:
             return
         msg = msgfmt % msgargs
+        opts = pycompat.byteskwargs(opts)
         # guard against recursion from e.g. ui.debug()
         registeredloggers = self._loggers
         self._loggers = {}