diff -u b/core/lib/Drupal/Component/PhpStorage/FileReadOnlyStorage.php b/core/lib/Drupal/Component/PhpStorage/FileReadOnlyStorage.php
--- b/core/lib/Drupal/Component/PhpStorage/FileReadOnlyStorage.php
+++ b/core/lib/Drupal/Component/PhpStorage/FileReadOnlyStorage.php
@@ -5,7 +5,7 @@
 /**
  * Reads code as regular PHP files, but won't write them.
  */
-class FileReadOnlyStorage extends PhpStorageBase implements PhpStorageInterface {
+class FileReadOnlyStorage extends PhpStorageBase {
 
   /**
    * The directory where the files should be stored.
diff -u b/core/lib/Drupal/Component/PhpStorage/FileStorage.php b/core/lib/Drupal/Component/PhpStorage/FileStorage.php
--- b/core/lib/Drupal/Component/PhpStorage/FileStorage.php
+++ b/core/lib/Drupal/Component/PhpStorage/FileStorage.php
@@ -7,7 +7,7 @@
 /**
  * Stores the code as regular PHP files.
  */
-class FileStorage extends PhpStorageBase implements PhpStorageInterface {
+class FileStorage extends PhpStorageBase {
 
   /**
    * The directory where the files should be stored.