diff --git a/openwisp_network_topology/templates/netjsongraph/netjsongraph-script.html b/openwisp_network_topology/templates/netjsongraph/netjsongraph-script.html
index 2fcbdea..c2ab4b2 100644
--- a/openwisp_network_topology/templates/netjsongraph/netjsongraph-script.html
+++ b/openwisp_network_topology/templates/netjsongraph/netjsongraph-script.html
@@ -4,7 +4,8 @@
     loadNetJsonGraph = (el='body', url='{{ graph_url }}?include_unpublished=true') => {
         const history_url = '{{ history_url }}?include_unpublished=true';
         const wsProtocol = window.location.protocol === 'https:' ? 'wss:' : 'ws:';
-        const wsUrl = `${wsProtocol}//${window.location.host}/ws/network-topology/topology/${getTopologyIdFromUrl()}/`;
+        const apiHost = new URL('{{ graph_url }}').host;
+        const wsUrl = `${wsProtocol}//${apiHost}/ws/network-topology/topology/${getTopologyIdFromUrl()}/`;
         const socket = new WebSocket(wsUrl);
 
         const getDataParseOptions = (data) => {