diff --git a/jquery.form.js b/jquery.form.js
index 13e9a55c..88f68cf0 100644
--- a/jquery.form.js
+++ b/jquery.form.js
@@ -537,7 +537,7 @@ $.fn.ajaxSubmit = function(options) {
                     s.dataType = 'xml';
                 xhr.getResponseHeader = function(header){
                     var headers = {'content-type': s.dataType};
-                    return headers[header];
+                    return headers[header.toLowerCase()];
                 };
                 // support for XHR 'status' & 'statusText' emulation :
                 if (docRoot) {