diff --git a/eventlet/websocket.py b/eventlet/websocket.py
index 194e984..7f3e048 100644
--- a/eventlet/websocket.py
+++ b/eventlet/websocket.py
@@ -40,7 +40,7 @@ class WebSocketWSGI(object):
 
     def __call__(self, environ, start_response):
         if not (environ.get('HTTP_CONNECTION') == 'Upgrade' and
-                environ.get('HTTP_UPGRADE') == 'WebSocket'):
+                environ.get('HTTP_UPGRADE').lower() == 'websocket'):
             # need to check a few more things here for true compliance
             start_response('400 Bad Request', [('Connection','close')])
             return []