diff --git a/lib/adapters/xhr.js b/lib/adapters/xhr.js
index 5da074dde9..67c28bd2c9 100644
--- a/lib/adapters/xhr.js
+++ b/lib/adapters/xhr.js
@@ -27,6 +27,10 @@ module.exports = function xhrAdapter(config) {
       }
     }
 
+    if (utils.isFormData(requestData)) {
+      delete requestHeaders['Content-Type']; // Let the browser set it
+    }
+
     var request = new XMLHttpRequest();
 
     // HTTP basic authentication