diff --git a/lib/proxy.js b/lib/proxy.js
index d835eb4..b35f2df 100644
--- a/lib/proxy.js
+++ b/lib/proxy.js
@@ -236,7 +236,7 @@ function bypass(req, res, params) {
       .pipe(res, { end: false });
   };
 
-  if (isNaN(length) || isFinite(length)) {
+  if (!isFinite(length)) {
     onEnd(params, res);
     return;
   }