diff --git a/src/EventSubscriber/CommerceSellOnceTransactionSubscriber.php b/src/EventSubscriber/CommerceSellOnceTransactionSubscriber.php
index 44d84cc..1092e78 100644
--- a/src/EventSubscriber/CommerceSellOnceTransactionSubscriber.php
+++ b/src/EventSubscriber/CommerceSellOnceTransactionSubscriber.php
@@ -32,7 +32,7 @@ class CommerceSellOnceTransactionSubscriber implements EventSubscriberInterface
   /**
    * @inheritDoc
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     return [
       SellOnceTransactionEvents::SELL_ONCE_TRANSACTION => 'onTransaction',
     ];