diff --git a/lib/http.js b/lib/http.js
index 47296080976..caeff0f2c7f 100644
--- a/lib/http.js
+++ b/lib/http.js
@@ -236,7 +236,7 @@ OutgoingMessage.prototype.sendHeaderLines = function (first_line, headers) {
   var message_header = first_line;
   var field, value;
   for (var i in headers) {
-    if (headers instanceof Array) {
+    if (headers[i] instanceof Array) {
       field = headers[i][0];
       value = headers[i][1];
     } else {