diff --git a/lib/application.js b/lib/application.js
index 9919d9930..1854f37af 100644
--- a/lib/application.js
+++ b/lib/application.js
@@ -200,9 +200,9 @@ function respond(ctx) {
   // allow bypassing koa
   if (false === ctx.respond) return;
 
-  const res = ctx.res;
   if (!ctx.writable) return;
 
+  const res = ctx.res;
   let body = ctx.body;
   const code = ctx.status;