diff --git a/lib/index.js b/lib/index.js
index f2b2956..24978ff 100644
--- a/lib/index.js
+++ b/lib/index.js
@@ -134,7 +134,7 @@ function processMultipart(options, req, res, next) {
         data: buf,
         encoding: encoding,
         mimetype: mime,
-        mv: function(path, callback = null) {
+        mv: function(path, callback) {
           // Callback is passed in, use the callback API
           if (callback) {
             doMove(