diff --git a/src/PhpWord/Style/Language.php b/src/PhpWord/Style/Language.php
index e47cceb3e9..c669ee4238 100644
--- a/src/PhpWord/Style/Language.php
+++ b/src/PhpWord/Style/Language.php
@@ -247,7 +247,9 @@ private function validateLocale($locale)
         if ($locale !== null && strlen($locale) === 2) {
             return strtolower($locale) . '-' . strtoupper($locale);
         }
-
+        if ($locale === 'und') {
+            return 'en-EN';
+        }
         if ($locale !== null && $locale !== 'zxx' && strstr($locale, '-') === false) {
             throw new InvalidArgumentException($locale . ' is not a valid language code');
         }