diff -r a150173da1c1 -r f1c9fafcbf46 mercurial/hgweb/hgweb_mod.py
--- a/mercurial/hgweb/hgweb_mod.py	Sun Dec 18 01:46:39 2016 +0530
+++ b/mercurial/hgweb/hgweb_mod.py	Sun Dec 18 01:54:36 2016 +0530
@@ -286,7 +286,8 @@
         Modern servers should be using WSGI and should avoid this
         method, if possible.
         """
-        if not os.environ.get('GATEWAY_INTERFACE', '').startswith("CGI/1."):
+        if not encoding.environ.get('GATEWAY_INTERFACE',
+                                    '').startswith("CGI/1."):
             raise RuntimeError("This function is only intended to be "
                                "called while running as a CGI script.")
         wsgicgi.launch(self)