diff -r 165a77f7ec13 -r e320d9405bba mercurial/hgweb/request.py
--- a/mercurial/hgweb/request.py	Wed Apr 11 14:57:11 2018 -0400
+++ b/mercurial/hgweb/request.py	Wed Apr 11 16:09:23 2018 -0400
@@ -518,8 +518,10 @@
                 if not chunk:
                     break
 
+        strheaders = [(pycompat.strurl(k), pycompat.strurl(v)) for
+                      k, v in self.headers.items()]
         write = self._startresponse(pycompat.sysstr(self.status),
-                                    self.headers.items())
+                                    strheaders)
 
         if self._bodybytes:
             yield self._bodybytes