diff --git a/mercurial/hgweb/wsgicgi.py b/mercurial/hgweb/wsgicgi.py
--- a/mercurial/hgweb/wsgicgi.py
+++ b/mercurial/hgweb/wsgicgi.py
@@ -23,7 +23,7 @@ def launch(application):
     environ['wsgi.multiprocess'] = True
     environ['wsgi.run_once'] = True
 
-    if environ.get('HTTPS','off') in ('on','1'):
+    if environ.get('HTTPS','off').lower() in ('on','1','yes'):
         environ['wsgi.url_scheme'] = 'https'
     else:
         environ['wsgi.url_scheme'] = 'http'