diff --git a/lib/adapters/xhr.js b/lib/adapters/xhr.js
index f44bd45..2ad7e3e 100644
--- a/lib/adapters/xhr.js
+++ b/lib/adapters/xhr.js
@@ -27,7 +27,7 @@ module.exports = function xhrAdapter(resolve, reject, config) {
 
   // Create the request
   var request = new(XMLHttpRequest || ActiveXObject)('Microsoft.XMLHTTP');
-  request.open(config.method, buildUrl(config.url, config.params), true);
+  request.open(config.method.toUpperCase(), buildUrl(config.url, config.params), true);
 
   // Listen for ready state
   request.onreadystatechange = function () {