--- a/src/Plugin/Field/FieldFormatter/FieldSlideshow.php
+++ b/src/Plugin/Field/FieldFormatter/FieldSlideshow.php
@@ -57,7 +57,7 @@
    *
    * @var \Drupal\Core\File\FileUrlGeneratorInterface
    */
-  protected $fileUrlGenerator;
+  protected FileUrlGeneratorInterface $fileUrlGenerator;

   /**
    * FieldSlideshow constructor.