diff --git a/modules/system/system.module b/modules/system/system.module
index 98df486..9f95a38 100644
--- a/modules/system/system.module
+++ b/modules/system/system.module
@@ -3740,7 +3740,7 @@ function system_date_format_save($date_format, $dfid = 0) {
   if (!empty($date_format['locales'])) {
     foreach ($date_format['locales'] as $langcode) {
       // Only proceed if language is enabled.
-      if (in_array($langcode, $languages)) {
+      if (isset($languages[$langcode])) {
         $is_existing = (bool) db_query_range('SELECT 1 FROM {date_format_locale} WHERE type = :type AND language = :language', 0, 1, array(':type' => $date_format['type'], ':language' => $langcode))->fetchField();
         if (!$is_existing) {
           $locale_format['language'] = $langcode;