diff --git a/lib/tfw/fsm_base.py b/lib/tfw/fsm_base.py
index 6557733..d6a586c 100644
--- a/lib/tfw/fsm_base.py
+++ b/lib/tfw/fsm_base.py
@@ -21,3 +21,6 @@ class FSMBase:
 
     def subscribe_message_handler(self, msghandler):
         self.message_handlers.append(msghandler)
+
+    def unsubscribe_message_handler(self, msghandler):
+        self.message_handlers.remove(msghandler)
diff --git a/lib/tfw/networking/server/zmq_websocket_handler.py b/lib/tfw/networking/server/zmq_websocket_handler.py
index e29304d..aa55382 100644
--- a/lib/tfw/networking/server/zmq_websocket_handler.py
+++ b/lib/tfw/networking/server/zmq_websocket_handler.py
@@ -49,6 +49,9 @@ class FSMManagingSocketHandler(ZMQWebSocketHandler):
             FSMManagingSocketHandler.fsm = FSM()
         self.fsm.subscribe_message_handler(self.handle_fsm_message)
 
+    def on_close(self):
+        self.fsm.unsubscribe_message_handler(self.handle_fsm_message)
+
     def handle_fsm_message(self, message):
         self._event_handler_connector.send_message(message)