diff --git a/lib/transports/polling.js b/lib/transports/polling.js
index 5d15c0763..47bf36bb6 100644
--- a/lib/transports/polling.js
+++ b/lib/transports/polling.js
@@ -154,12 +154,12 @@ Polling.prototype.onDataRequest = function (req, res) {
 
   function onData (data) {
     var contentLength;
-    if (typeof data === 'string') {
-      chunks += data;
-      contentLength = Buffer.byteLength(chunks);
-    } else {
+    if (isBinary) {
       chunks = Buffer.concat([chunks, data]);
       contentLength = chunks.length;
+    } else {
+      chunks += data;
+      contentLength = Buffer.byteLength(chunks);
     }
 
     if (contentLength > self.maxHttpBufferSize) {