diff --git a/frontend/next.config.ts b/frontend/next.config.ts
index 6bd62bd..c6c37fb 100644
--- a/frontend/next.config.ts
+++ b/frontend/next.config.ts
@@ -1,6 +1,18 @@
 import type { NextConfig } from "next";
 
+// Hosts allowed to load /_next/* dev resources from this dev server.
+// Next.js 16 blocks cross-origin dev requests by default; without this,
+// running `next dev` behind any reverse proxy or non-localhost origin
+// silently breaks HMR and React hydration.
+// Set ALLOWED_DEV_ORIGINS as a comma-separated list, e.g.
+//   ALLOWED_DEV_ORIGINS=bigset.example.com,staging.example.com
+const allowedDevOrigins = (process.env.ALLOWED_DEV_ORIGINS || "")
+  .split(",")
+  .map((s) => s.trim())
+  .filter(Boolean);
+
 const nextConfig: NextConfig = {
+  allowedDevOrigins,
   async rewrites() {
     return [
       {