diff --git a/src/EventSubscriber/CspSubscriber.php b/src/EventSubscriber/CspSubscriber.php
index 98ee91f..8dd9df1 100644
--- a/src/EventSubscriber/CspSubscriber.php
+++ b/src/EventSubscriber/CspSubscriber.php
@@ -16,7 +16,7 @@ class CspSubscriber implements EventSubscriberInterface {
   /**
    * {@inheritdoc}
    */
-  public static function getSubscribedEvents() {
+  public static function getSubscribedEvents(): array {
     if (!class_exists(CspEvents::class)) {
       return [];
     }