diff --git a/lib/transports/polling-xhr.js b/lib/transports/polling-xhr.js
index dbf000f43..b2576636b 100755
--- a/lib/transports/polling-xhr.js
+++ b/lib/transports/polling-xhr.js
@@ -205,7 +205,7 @@ Request.prototype.create = function () {
         }
       }
     } catch (e) {}
-    if (this.supportsBinary) {
+    if (this.supportsBinary && this.isBinary) {
       // This has to be done after open because Firefox is stupid
       // http://stackoverflow.com/questions/13216903/get-binary-data-with-xmlhttprequest-in-a-firefox-extension
       xhr.responseType = 'arraybuffer';