diff --git a/README.md b/README.md
index 27fa73e..63fa337 100644
--- a/README.md
+++ b/README.md
@@ -157,12 +157,13 @@ router
     return NextResponse.json({ user });
   });
 
+// Make sure to cast the handler return to `Promise<NextResponse>` to prevent type error with next.js 14 app router in production/preview deployments.
 export async function GET(request: NextRequest, ctx: RequestContext) {
-  return router.run(request, ctx);
+  return router.run(request, ctx) as Promise<NextResponse>;
 }
 
 export async function PUT(request: NextRequest, ctx: RequestContext) {
-  return router.run(request, ctx);
+  return router.run(request, ctx) as Promise<NextResponse>;
 }
 ```