diff --git a/lib/tfw/networking/server/zmq_websocket_proxy.py b/lib/tfw/networking/server/zmq_websocket_proxy.py
index fc12a6c..15826bd 100644
--- a/lib/tfw/networking/server/zmq_websocket_proxy.py
+++ b/lib/tfw/networking/server/zmq_websocket_proxy.py
@@ -65,9 +65,10 @@ class ZMQWebSocketProxy(WebSocketHandler):
         LOG.debug('Received on pull socket: %s', message)
         self.proxy_eventhandler_to_websocket(message)
 
-    def sequence_message(self, message):
-        self.sequence_number += 1
-        message['seq'] = self.sequence_number
+    @classmethod
+    def sequence_message(cls, message):
+        cls.sequence_number += 1
+        message['seq'] = cls.sequence_number
 
     def on_message(self, message):
         """