diff --git a/package.json b/package.json
index 1ee3f7aad..031a074a5 100644
--- a/package.json
+++ b/package.json
@@ -51,6 +51,7 @@
   "devDependencies": {
     "@biomejs/biome": "^2.3.8",
     "@mariozechner/mini-lit": "0.2.1",
+    "@types/ws": "^8.5.12",
     "@types/body-parser": "^1.19.6",
     "@types/express": "^5.0.6",
     "@types/node": "^24.10.1",
diff --git a/src/webchat/server.ts b/src/webchat/server.ts
index d980ed314..7627bc358 100644
--- a/src/webchat/server.ts
+++ b/src/webchat/server.ts
@@ -405,7 +405,7 @@ export async function startWebChatServer(port = WEBCHAT_DEFAULT_PORT) {
         return;
       }
       const sessionKey = url.searchParams.get("session") ?? "main";
-      wss!.handleUpgrade(req, socket, head, (ws) => {
+      wss!.handleUpgrade(req, socket, head, (ws: WebSocket) => {
         ws.on("close", () => {
           const set = wsSessions.get(sessionKey);
           if (set) {
@@ -485,4 +485,3 @@ export async function ensureWebChatServerFromConfig() {
     throw err;
   }
 }
-*** End