diff --git a/mercurial/hgweb/hgweb_mod.py b/mercurial/hgweb/hgweb_mod.py
--- a/mercurial/hgweb/hgweb_mod.py
+++ b/mercurial/hgweb/hgweb_mod.py
@@ -651,12 +651,12 @@ class hgweb(object):
         return p
 
     def run(self):
-        if os.environ['GATEWAY_INTERFACE'][0:6] != "CGI/1.":
+        if not os.environ.get('GATEWAY_INTERFACE', '').startswith("CGI/1."):
             raise RuntimeError("This function is only intended to be called while running as a CGI script.")
         import mercurial.hgweb.wsgicgi as wsgicgi
         from request import wsgiapplication
         def make_web_app():
-            return self.__class__(self.repo, self.reponame)
+            return self
         wsgicgi.launch(wsgiapplication(make_web_app))
 
     def run_wsgi(self, req):