diff --git a/webui/src/lib/bootstrap.ts b/webui/src/lib/bootstrap.ts
index b7fafef9..d65c2b16 100644
--- a/webui/src/lib/bootstrap.ts
+++ b/webui/src/lib/bootstrap.ts
@@ -116,7 +116,15 @@ export function deriveWsUrl(
     const host = window.location.hostname.includes(":")
       ? `[${window.location.hostname}]`
       : window.location.hostname;
-    return `ws://${host}:8765${path}${query}`;
+    let scheme = "ws";
+    let port = "8765";
+    if (wsUrl && /^wss?:\/\//i.test(wsUrl)) {
+      const upstream = new URL(wsUrl);
+      scheme = upstream.protocol === "wss:" ? "wss" : "ws";
+      port = upstream.port;
+    }
+    const authority = port ? `${host}:${port}` : host;
+    return `${scheme}://${authority}${path}${query}`;
   }
   if (wsUrl && /^(wss?|nanobot-host):\/\//i.test(wsUrl)) {
     const join = wsUrl.includes("?") ? "&" : "?";
diff --git a/webui/src/tests/bootstrap.test.ts b/webui/src/tests/bootstrap.test.ts
index 1378ff50..6ee98bbf 100644
--- a/webui/src/tests/bootstrap.test.ts
+++ b/webui/src/tests/bootstrap.test.ts
@@ -32,6 +32,19 @@ describe("bootstrap helpers", () => {
     );
   });
 
+  it("keeps the gateway websocket port when Vite proxies a custom target", () => {
+    vi.stubGlobal("window", {
+      location: {
+        port: "5173",
+        hostname: "127.0.0.1",
+        protocol: "http:",
+      },
+    });
+    expect(deriveWsUrl("/ws", "tok", "ws://127.0.0.1:8899/ws")).toBe(
+      "ws://127.0.0.1:8899/ws?token=tok",
+    );
+  });
+
   it("preserves the host socket bridge URL", () => {
     expect(deriveWsUrl("/", "tok en", "nanobot-host://engine/")).toBe(
       "nanobot-host://engine/?token=tok%20en",