diff --git a/lib/http-proxy/common.js b/lib/http-proxy/common.js
index bcc7b8e87..52cb0ff7c 100644
--- a/lib/http-proxy/common.js
+++ b/lib/http-proxy/common.js
@@ -53,8 +53,7 @@ common.setupOutgoing = function(outgoing, options, req, forward) {
   if (!outgoing.agent) {
     outgoing.headers = outgoing.headers || {};
     if (typeof outgoing.headers.connection !== 'string'
-        || !outgoing.headers.connection.toLowerCase().split(',').some(
-          function (s) { if (s.trim() === 'upgrade') { return true; } })
+        || ! /(^|,)\s*upgrade\s*($|,)/i.test(outgoing.headers.connection)
        ) { outgoing.headers.connection = 'close'; }
   }