diff --git a/core/lib/Drupal/Core/DrupalKernel.php b/core/lib/Drupal/Core/DrupalKernel.php
index 0ef88be..a232757 100644
--- a/core/lib/Drupal/Core/DrupalKernel.php
+++ b/core/lib/Drupal/Core/DrupalKernel.php
@@ -16,7 +16,6 @@
 use Drupal\Core\File\MimeType\MimeTypeGuesser;
 use Drupal\Core\Http\TrustedHostsRequestFactory;
 use Drupal\Core\Language\Language;
-use Drupal\Core\Session\AccountProxyInitializedInterface;
 use Drupal\Core\Site\Settings;
 use Symfony\Cmf\Component\Routing\RouteObjectInterface;
 use Symfony\Component\DependencyInjection\ContainerInterface;
@@ -783,12 +782,7 @@ protected function initializeContainer() {
       if ($this->container->initialized('current_user')) {
         $current_user = $this->container->get('current_user');
         // Ensure to not accidentally initialize the user.
-        if ($current_user instanceof AccountProxyInitializedInterface) {
-          $current_user_id = $current_user->accountIsInitialized() ? $current_user->id() : 0;
-        }
-        else {
-          $current_user_id = $current_user->id();
-        }
+        $current_user_id = $current_user->accountIsInitialized() ? $current_user->id() : 0;
       }
 
       // If there is a session, close and save it.
diff --git a/core/lib/Drupal/Core/Extension/ModuleInstaller.php b/core/lib/Drupal/Core/Extension/ModuleInstaller.php
index 7d24f74..ef41a0f 100644
--- a/core/lib/Drupal/Core/Extension/ModuleInstaller.php
+++ b/core/lib/Drupal/Core/Extension/ModuleInstaller.php
@@ -182,7 +182,7 @@ public function install(array $module_list, $enable_dependencies = TRUE) {
         $this->moduleHandler->load($module);
         module_load_install($module);
 
-        // Clear the static cache of ModuleExtensionList to pick up the
+        // Clear the static cache of module_listing to pick up the
         // new module, since it merges the installation status of modules into
         // its statically cached list.
         \Drupal::service('module_listing')->reset();
@@ -437,7 +437,7 @@ public function uninstall(array $module_list, $uninstall_dependents = TRUE) {
       // Remove any potential cache bins provided by the module.
       $this->removeCacheBins($module);
 
-      // Clear the static cache of ModuleExtensionList to pick up the
+      // Clear the static cache of module_listing to pick up the
       // new module, since it merges the installation status of modules into
       // its statically cached list.
       \Drupal::service('module_listing')->reset();
diff --git a/core/lib/Drupal/Core/Session/AccountProxy.php b/core/lib/Drupal/Core/Session/AccountProxy.php
index 72d03a3..63cf9a1 100644
--- a/core/lib/Drupal/Core/Session/AccountProxy.php
+++ b/core/lib/Drupal/Core/Session/AccountProxy.php
@@ -13,7 +13,7 @@
  * allows legacy code to change the current user where the user cannot be
  * directly injected into dependent code.
  */
-class AccountProxy implements AccountProxyInterface, AccountProxyInitializedInterface {
+class AccountProxy implements AccountProxyInterface {
 
   /**
    * The instantiated account.
diff --git a/core/lib/Drupal/Core/Session/AccountProxyInitializedInterface.php b/core/lib/Drupal/Core/Session/AccountProxyInitializedInterface.php
deleted file mode 100644
index 007a8c2..0000000
--- a/core/lib/Drupal/Core/Session/AccountProxyInitializedInterface.php
+++ /dev/null
@@ -1,18 +0,0 @@
-<?php
-
-namespace Drupal\Core\Session;
-
-/**
- * Extends the account proxy interface with a "is initialized" method.
- */
-interface AccountProxyInitializedInterface extends AccountProxyInterface {
-
-  /**
-   * Returns whether the account is already initialized.
-   *
-   * @return bool
-   *   TRUE, when the account was initialized already.
-   */
-  public function accountIsInitialized();
-
-}
diff --git a/core/lib/Drupal/Core/Session/AccountProxyInterface.php b/core/lib/Drupal/Core/Session/AccountProxyInterface.php
index 378b89d..8969bb2 100644
--- a/core/lib/Drupal/Core/Session/AccountProxyInterface.php
+++ b/core/lib/Drupal/Core/Session/AccountProxyInterface.php
@@ -43,4 +43,12 @@ public function getAccount();
    */
   public function setInitialAccountId($account_id);
 
+  /**
+   * Returns whether the account is already initialized.
+   *
+   * @return bool
+   *   TRUE, when the account was initialized already.
+   */
+  public function accountIsInitialized();
+
 }