diff --git a/controller/index.html b/controller/index.html
index 48d7013..01ef7a8 100644
--- a/controller/index.html
+++ b/controller/index.html
@@ -370,7 +370,7 @@
 
   <script>
     // ---- WebSocket ----
-    const WS_URL = `ws://${location.host}/ws`;
+    const WS_URL = `${location.protocol === 'https:' ? 'wss:' : 'ws:'}//${location.host}/ws`;
     let ws = null;
     let currentState = {};
     let reconnectTimer = null;