--- a/mercurial/cmdutil.py	Sun May 14 09:38:06 2017 -0700
+++ b/mercurial/cmdutil.py	Thu May 04 00:24:21 2017 +0530
@@ -1496,6 +1496,7 @@
         props['index'] = next(self._counter)
         props['revcache'] = {'copies': copies}
         props['cache'] = self.cache
+        props = pycompat.strkwargs(props)
 
         # write header
         if self._parts['header']: