diff --git a/flask_socketio/__init__.py b/flask_socketio/__init__.py
index 090c7c0c..97153239 100644
--- a/flask_socketio/__init__.py
+++ b/flask_socketio/__init__.py
@@ -36,6 +36,7 @@ def __init__(self, socketio_app, flask_app, socketio_path='socket.io'):
                                                   socketio_path)
 
     def __call__(self, environ, start_response):
+        environ = environ.copy()
         environ['flask.app'] = self.flask_app
         return super(_SocketIOMiddleware, self).__call__(environ,
                                                          start_response)