diff --git a/lib/multipart.js b/lib/multipart.js
index 482cb2e..9ffe27a 100644
--- a/lib/multipart.js
+++ b/lib/multipart.js
@@ -15,7 +15,7 @@ const multipart = function (opts) {
   });
 
   multipart.push({
-    'content-type': mime.lookup(fileName),
+    'content-type': mime.getType(fileName),
     'content-disposition':
       'form-data; name="' + name + '"; filename="' + fileName + '"',
     body: opts.sobject.getBody()