diff -r c1de7efca574 -r cd6ae9ab7bd8 mercurial/hgweb/hgwebdir_mod.py
--- a/mercurial/hgweb/hgwebdir_mod.py	Sun Mar 11 15:40:58 2018 -0700
+++ b/mercurial/hgweb/hgwebdir_mod.py	Sun Mar 11 15:55:38 2018 -0700
@@ -367,7 +367,6 @@
             csp, nonce = cspvalues(self.ui)
             if csp:
                 res.headers['Content-Security-Policy'] = csp
-                wsgireq.headers.append(('Content-Security-Policy', csp))
 
             virtual = req.dispatchpath.strip('/')
             tmpl = self.templater(req, nonce)