diff --git a/src/Infrastructure/System/Clock.php b/src/Infrastructure/System/Clock.php
index 5f7edf3..169d204 100644
--- a/src/Infrastructure/System/Clock.php
+++ b/src/Infrastructure/System/Clock.php
@@ -8,6 +8,7 @@
 namespace JeckelLab\Contract\Infrastructure\System;
 
 use DateTimeImmutable;
+use DateTimeZone;
 
 /**
  * Interface Clock
@@ -16,7 +17,8 @@
 interface Clock
 {
     /**
+     * @param DateTimeZone|null $timezone
      * @return DateTimeImmutable
      */
-    public function now(): DateTimeImmutable;
+    public function now(?DateTimeZone $timezone = null): DateTimeImmutable;
 }