diff --git a/src/components/LoginScreen.tsx b/src/components/LoginScreen.tsx
index 0119731..24eca4e 100644
--- a/src/components/LoginScreen.tsx
+++ b/src/components/LoginScreen.tsx
@@ -12,7 +12,18 @@ interface Props {
 function getInitialUrl(): string {
   const stored = getStoredCredentials();
   if (stored) return stored.url;
-  return import.meta.env.VITE_GATEWAY_WS_URL || `ws://${window.location.hostname}:18789`;
+  if (import.meta.env.VITE_GATEWAY_WS_URL) return import.meta.env.VITE_GATEWAY_WS_URL;
+  const protocol = window.location.protocol === 'https:' ? 'wss' : 'ws';
+  const host = window.location.hostname;
+  // When served over HTTPS, assume gateway is on a sibling subdomain (e.g. marlbot-gw.example.com)
+  if (protocol === 'wss') {
+    const parts = host.split('.');
+    if (parts.length >= 2) {
+      parts[0] = parts[0] + '-gw';
+      return `${protocol}://${parts.join('.')}`;
+    }
+  }
+  return `${protocol}://${host}:18789`;
 }
 
 function getInitialToken(): string {