--- a/mercurial/hgweb/hgweb_mod.py	Mon Oct 16 18:58:16 2017 +0200
+++ b/mercurial/hgweb/hgweb_mod.py	Mon Oct 16 22:43:19 2017 -0400
@@ -187,7 +187,7 @@
         if style == styles[0]:
             vars['style'] = style
 
-        start = r'&' if req.url[-1] == r'?' else r'?'
+        start = '&' if req.url[-1] == r'?' else '?'
         sessionvars = webutil.sessionvars(vars, start)
 
         if not self.reponame: