diff --git a/src/Elements/IODEFDocument.php b/src/Elements/IODEFDocument.php
index <HASH>..<HASH> 100644
--- a/src/Elements/IODEFDocument.php
+++ b/src/Elements/IODEFDocument.php
@@ -16,7 +16,7 @@ class IODEFDocument extends IodefElement
     {
         $this->attributes = [
             'version'   => '1.00',
-            'lang'      => 'en',
+            'lang'      => 'en-US',
             'formatid'  => '',
         ];
Fixed default language

The default language was set in an incorrect format.