diff --git a/hgext/churn.py b/hgext/churn.py
--- a/hgext/churn.py
+++ b/hgext/churn.py
@@ -52,7 +52,7 @@
         def getkey(ctx):
             t, tz = ctx.date()
             date = datetime.datetime(*time.gmtime(float(t) - tz)[:6])
-            return date.strftime(opts['dateformat'])
+            return date.strftime(pycompat.sysstr(opts['dateformat']))
     else:
         tmpl = opts.get('oldtemplate') or opts.get('template')
         tmpl = logcmdutil.maketemplater(ui, repo, tmpl)