diff --git a/server.js b/server.js
index 617a02e..701772f 100644
--- a/server.js
+++ b/server.js
@@ -47,8 +47,13 @@ const PORT = process.env.PORT || 3000;
 // ──────────────────────────────────────────────────────────────────────────────
 app.set('trust proxy', 1); // Required for rate-limiter behind proxies/load balancers
 
+const allowedOrigins = (process.env.ALLOWED_ORIGINS || process.env.APP_URL || '*').split(',');
+
 app.use(cors({
-  origin:      process.env.APP_URL || '*',
+  origin:      (origin, callback) => {
+    if (!origin || allowedOrigins.includes(origin)) return callback(null, true);
+    callback(new Error(`CORS: origin ${origin} not allowed`));
+  },
   credentials: true,
 }));