diff --git a/Utils/Barcode/C128Abstract.php b/Utils/Barcode/C128Abstract.php
index dea55dcd5..3119214a1 100644
--- a/Utils/Barcode/C128Abstract.php
+++ b/Utils/Barcode/C128Abstract.php
@@ -273,7 +273,7 @@ abstract class C128Abstract
      *
      * @since  1.0.0
      */
-    public function isValidString(string $barcode) : bool
+    public static function isValidString(string $barcode) : bool
     {
         $length = \strlen($barcode);