diff --git a/src/Plugin/PdfBackend/LocalServerPdfBackend.php b/src/Plugin/PdfBackend/LocalServerPdfBackend.php
index 3a09449f9b8848fb05c07009f15dbe0afbbb8c44..3882c8488d9536da8a4f051751458b699503ff3c 100644
--- a/src/Plugin/PdfBackend/LocalServerPdfBackend.php
+++ b/src/Plugin/PdfBackend/LocalServerPdfBackend.php
@@ -28,7 +28,7 @@ class LocalServerPdfBackend extends PdfBackendBase implements ContainerFactoryPl
   /**
    * The file system.
    *
-   * @var \Drupal\Core\File\FileSystem
+   * @var \Drupal\Core\File\FileSystemInterface
    */
   protected $fileSystem;
 
diff --git a/src/Plugin/PdfBackend/PdftkPdfBackend.php b/src/Plugin/PdfBackend/PdftkPdfBackend.php
index f9c4491feb6aabda0b28effba774f236bfee7f45..716e1afd03730e03cef57b22d0027cb863170204 100644
--- a/src/Plugin/PdfBackend/PdftkPdfBackend.php
+++ b/src/Plugin/PdfBackend/PdftkPdfBackend.php
@@ -3,7 +3,6 @@
 namespace Drupal\fillpdf\Plugin\PdfBackend;
 
 use Drupal\Core\Entity\EntityTypeManagerInterface;
-use Drupal\Core\File\FileSystem;
 use Drupal\Core\File\FileSystemInterface;
 use Drupal\Core\Plugin\ContainerFactoryPluginInterface;
 use Drupal\file\FileInterface;
@@ -35,7 +34,7 @@ class PdftkPdfBackend extends PdfBackendBase implements ContainerFactoryPluginIn
   /**
    * The file system.
    *
-   * @var \Drupal\Core\File\FileSystem
+   * @var \Drupal\Core\File\FileSystemInterface
    */
   protected $fileSystem;
 
@@ -62,14 +61,14 @@ class PdftkPdfBackend extends PdfBackendBase implements ContainerFactoryPluginIn
    *   The plugin_id for the plugin instance.
    * @param array $plugin_definition
    *   The plugin implementation definition.
-   * @param \Drupal\Core\File\FileSystem $file_system
+   * @param \Drupal\Core\File\FileSystemInterface $file_system
    *   The file system.
    * @param \Drupal\fillpdf\ShellManager $shell_manager
    *   The FillPDF shell manager.
    * @param \Drupal\Core\Entity\EntityTypeManagerInterface $entity_type_manager
    *   The entity type manager.
    */
-  public function __construct(array $configuration, $plugin_id, array $plugin_definition, FileSystem $file_system, ShellManager $shell_manager, EntityTypeManagerInterface $entity_type_manager) {
+  public function __construct(array $configuration, $plugin_id, array $plugin_definition, FileSystemInterface $file_system, ShellManager $shell_manager, EntityTypeManagerInterface $entity_type_manager) {
     parent::__construct($configuration, $plugin_id, $plugin_definition);
     $this->fileSystem = $file_system;
     $this->shellManager = $shell_manager;
diff --git a/tests/src/Traits/TestFillPdfTrait.php b/tests/src/Traits/TestFillPdfTrait.php
index 8b5e846dc0afa874bbb6874c6cdee5948d2fd4c8..b00b726f4156e595eef0227d5b586df381e0c3b5 100644
--- a/tests/src/Traits/TestFillPdfTrait.php
+++ b/tests/src/Traits/TestFillPdfTrait.php
@@ -146,7 +146,7 @@ trait TestFillPdfTrait {
    *   The absolute locale filepath or FALSE on failure.
    */
   protected function getTestPdfPath($filename) {
-    /** @var \Drupal\Core\File\FileSystem $file_system */
+    /** @var \Drupal\Core\File\FileSystemInterface $file_system */
     $file_system = $this->container->get('file_system');
     return $file_system->realpath(\Drupal::service('extension.list.module')->getPath('fillpdf') . '/tests/modules/fillpdf_test/files/' . $filename);
   }