diff --git a/api/src/Mail.php b/api/src/Mail.php
index 11f3a4512c..0963139b52 100644
--- a/api/src/Mail.php
+++ b/api/src/Mail.php
@@ -6407,7 +6407,7 @@ class Mail
 	 * @param string $filename
 	 * @return Cleaned filename, with problematic characters replaced with '_'.
 	 */
-	protected static function clean_subject_for_filename($filename)
+	static function clean_subject_for_filename($filename)
 	{
 		static $filter_pattern = '$[\f\n\t\v\\:*#?<>%"\|/\\\?]$';
 		return preg_replace($filter_pattern, "_", trim($filename));