diff --git a/src/StepCode.php b/src/StepCode.php
index 2d92f90..ac1dfd7 100644
--- a/src/StepCode.php
+++ b/src/StepCode.php
@@ -6,10 +6,10 @@
 
 use Kiboko\Contract\Pipeline\StepCodeInterface;
 
-final class StepCode implements StepCodeInterface
+final readonly class StepCode implements StepCodeInterface
 {
     private function __construct(
-        private readonly string $reference,
+        private string $reference,
     ) {
     }