diff --git a/src/Projectionist.php b/src/Projectionist.php
index 030cc019..e7e5af68 100644
--- a/src/Projectionist.php
+++ b/src/Projectionist.php
@@ -319,7 +319,7 @@ public function isReplaying(): bool
     public function replay(
         Collection $projectors,
         int $startingFromEventId = 0,
-        callable $onEventReplayed = null,
+        ?callable $onEventReplayed = null,
         ?string $aggregateUuid = null
     ): void {
         $projectors = (new EventHandlerCollection($projectors))