diff --git a/r4032login.info.yml b/r4032login.info.yml
index 6f0da3e..5fe1a48 100644
--- a/r4032login.info.yml
+++ b/r4032login.info.yml
@@ -1,5 +1,6 @@
 name: 'Redirect 403 to User Login'
-type: module
 description: 'Redirect anonymous users from 403 Access Denied pages to the /user/login page.'
-core: 8.x
+core_version_requirement: ^8.8 || ^9
+type: module
+
 configure: system.site_information_settings
diff --git a/r4032login.services.yml b/r4032login.services.yml
index ae25815..7e2bc86 100644
--- a/r4032login.services.yml
+++ b/r4032login.services.yml
@@ -1,6 +1,6 @@
 services:
   r4032login.subscriber:
     class: Drupal\r4032login\EventSubscriber\R4032LoginSubscriber
-    arguments: ['@config.factory', '@current_user', '@request_stack', '@path.matcher', '@event_dispatcher']
+    arguments: ['@config.factory', '@current_user', '@request_stack', '@path.matcher', '@event_dispatcher', '@messenger']
     tags:
       - { name: event_subscriber }
diff --git a/src/EventSubscriber/R4032LoginSubscriber.php b/src/EventSubscriber/R4032LoginSubscriber.php
index 6f9b5f1..50cdd8c 100644
--- a/src/EventSubscriber/R4032LoginSubscriber.php
+++ b/src/EventSubscriber/R4032LoginSubscriber.php
@@ -5,6 +5,7 @@ namespace Drupal\r4032login\EventSubscriber;
 use Drupal\Component\Utility\UrlHelper;
 use Drupal\Core\Config\ConfigFactoryInterface;
 use Drupal\Core\EventSubscriber\HttpExceptionSubscriberBase;
+use Drupal\Core\Messenger\MessengerInterface;
 use Drupal\Core\Path\PathMatcherInterface;
 use Drupal\Core\Routing\TrustedRedirectResponse;
 use Drupal\Core\Session\AccountInterface;
@@ -56,6 +57,13 @@ class R4032LoginSubscriber extends HttpExceptionSubscriberBase {
    */
   protected $eventDispatcher;
 
+  /**
+   * The messenger service.
+   *
+   * @var \Drupal\Core\Messenger\MessengerInterface
+   */
+  protected $messenger;
+
   /**
    * Constructs a new R4032LoginSubscriber.
    *
@@ -69,13 +77,16 @@ class R4032LoginSubscriber extends HttpExceptionSubscriberBase {
    *   The path matcher.
    * @param \Symfony\Component\EventDispatcher\EventDispatcherInterface $event_dispatcher
    *   The event dispatcher.
+   * @param \Drupal\Core\Messenger\MessengerInterface $messenger
+   *   The messenger service.
    */
-  public function __construct(ConfigFactoryInterface $config_factory, AccountInterface $current_user, RequestStack $request_stack, PathMatcherInterface $path_matcher, EventDispatcherInterface $event_dispatcher) {
+  public function __construct(ConfigFactoryInterface $config_factory, AccountInterface $current_user, RequestStack $request_stack, PathMatcherInterface $path_matcher, EventDispatcherInterface $event_dispatcher, MessengerInterface $messenger) {
     $this->configFactory = $config_factory;
     $this->currentUser = $current_user;
     $this->requestStack = $request_stack;
     $this->pathMatcher = $path_matcher;
     $this->eventDispatcher = $event_dispatcher;
+    $this->messenger = $messenger;
   }
 
   /**
@@ -160,7 +171,7 @@ class R4032LoginSubscriber extends HttpExceptionSubscriberBase {
         if ($this->currentUser->isAnonymous() && $config->get('display_denied_message')) {
           $message = $config->get('access_denied_message');
           $messageType = $config->get('access_denied_message_type');
-          drupal_set_message(Xss::filterAdmin($message), $messageType);
+          $this->messenger->addMessage(Xss::filterAdmin($message), $messageType);
         }
 
         if ($redirectPath === '<front>') {
diff --git a/tests/src/Unit/R4032LoginSubscriberTest.php b/tests/src/Unit/R4032LoginSubscriberTest.php
index e06bd2a..2f06cd6 100644
--- a/tests/src/Unit/R4032LoginSubscriberTest.php
+++ b/tests/src/Unit/R4032LoginSubscriberTest.php
@@ -62,6 +62,13 @@ namespace Drupal\Tests\r4032login\Unit {
      */
     protected $eventDispatcher;
 
+    /**
+     * The messenger service.
+     *
+     * @var \Drupal\Core\Messenger\MessengerInterface
+     */
+    protected $messenger;
+
     /**
      * The mocked unrouted URL assembler.
      *
@@ -80,7 +87,7 @@ namespace Drupal\Tests\r4032login\Unit {
      * {@inheritdoc}
      */
     protected function setUp() {
-      $this->kernel = $this->getMock('Symfony\Component\HttpKernel\HttpKernelInterface');
+      $this->kernel = $this->createMock('Symfony\Component\HttpKernel\HttpKernelInterface');
       $this->configFactory = $this->getConfigFactoryStub([
         'r4032login.settings' => [
           'display_denied_message' => TRUE,
@@ -92,20 +99,21 @@ namespace Drupal\Tests\r4032login\Unit {
           'match_noredirect_pages' => '',
         ],
       ]);
-      $this->currentUser = $this->getMock('Drupal\Core\Session\AccountInterface');
+      $this->currentUser = $this->createMock('Drupal\Core\Session\AccountInterface');
 
       $this->requestStack = new RequestStack();
       $this->requestStack->push(new Request());
 
-      $this->pathMatcher = $this->getMock('\Drupal\Core\Path\PathMatcherInterface');
-      $this->eventDispatcher = $this->getMock('\Symfony\Component\EventDispatcher\EventDispatcherInterface');
+      $this->pathMatcher = $this->createMock('\Drupal\Core\Path\PathMatcherInterface');
+      $this->eventDispatcher = $this->createMock('\Symfony\Component\EventDispatcher\EventDispatcherInterface');
+      $this->messenger = $this->createMock('\Drupal\Core\Messenger\MessengerInterface');
 
-      $this->urlAssembler = $this->getMock('Drupal\Core\Utility\UnroutedUrlAssemblerInterface');
+      $this->urlAssembler = $this->createMock('Drupal\Core\Utility\UnroutedUrlAssemblerInterface');
       $this->urlAssembler->expects($this->any())->method('assemble')->will($this->returnArgument(0));
-      $this->router = $this->getMock('Drupal\Tests\Core\Routing\TestRouterInterface');
+      $this->router = $this->createMock('Drupal\Tests\Core\Routing\TestRouterInterface');
 
       $container = new ContainerBuilder();
-      $container->set('path.validator', $this->getMock('Drupal\Core\Path\PathValidatorInterface'));
+      $container->set('path.validator', $this->createMock('Drupal\Core\Path\PathValidatorInterface'));
       $container->set('router.no_access_checks', $this->router);
       $container->set('unrouted_url_assembler', $this->urlAssembler);
       \Drupal::setContainer($container);
@@ -117,7 +125,7 @@ namespace Drupal\Tests\r4032login\Unit {
      * @covers ::__construct
      */
     public function testConstruct() {
-      $r4032login = new R4032LoginSubscriber($this->configFactory, $this->currentUser, $this->requestStack, $this->pathMatcher, $this->eventDispatcher);
+      $r4032login = new R4032LoginSubscriber($this->configFactory, $this->currentUser, $this->requestStack, $this->pathMatcher, $this->eventDispatcher, $this->messenger);
       $this->assertInstanceOf('\Drupal\r4032login\EventSubscriber\R4032LoginSubscriber', $r4032login);
     }
 
@@ -141,7 +149,7 @@ namespace Drupal\Tests\r4032login\Unit {
       ]);
       $this->currentUser->expects($this->any())->method('isAnonymous')->willReturn(TRUE);
 
-      $r4032login = new R4032LoginSubscriber($config, $this->currentUser, $this->requestStack, $this->pathMatcher, $this->eventDispatcher);
+      $r4032login = new R4032LoginSubscriber($config, $this->currentUser, $this->requestStack, $this->pathMatcher, $this->eventDispatcher, $this->messenger);
       $event = new GetResponseForExceptionEvent($this->kernel, $request, HttpKernelInterface::MASTER_REQUEST, new AccessDeniedHttpException());
       $dispatcher = new EventDispatcher();
       $dispatcher->addListener(KernelEvents::EXCEPTION, [
@@ -175,7 +183,7 @@ namespace Drupal\Tests\r4032login\Unit {
       ]);
       $this->currentUser->expects($this->any())->method('isAuthenticated')->willReturn(TRUE);
 
-      $r4032login = new R4032LoginSubscriber($config, $this->currentUser, $this->requestStack, $this->pathMatcher, $this->eventDispatcher);
+      $r4032login = new R4032LoginSubscriber($config, $this->currentUser, $this->requestStack, $this->pathMatcher, $this->eventDispatcher, $this->messenger);
       $event = new GetResponseForExceptionEvent($this->kernel, $request, HttpKernelInterface::MASTER_REQUEST, new AccessDeniedHttpException());
       $dispatcher = new EventDispatcher();
       $dispatcher->addListener(KernelEvents::EXCEPTION, [
@@ -253,13 +261,13 @@ namespace Drupal\Tests\r4032login\Unit {
      *   An array of GetResponseForExceptionEvent exception events.
      */
     public function providerInvalidExceptions() {
-      $kernel = $this->getMock('Symfony\Component\HttpKernel\HttpKernelInterface');
+      $kernel = $this->createMock('Symfony\Component\HttpKernel\HttpKernelInterface');
       $exceptions = [];
       foreach (get_declared_classes() as $name) {
         $class = new \ReflectionClass($name);
         if ($class->isSubclassOf('Exception')) {
           $exceptions[] = [
-            new GetResponseForExceptionEvent($kernel, new Request(), HttpKernelInterface::MASTER_REQUEST, $this->getMockBuilder($name)->disableOriginalConstructor()->getMock()),
+            new GetResponseForExceptionEvent($kernel, new Request(), HttpKernelInterface::MASTER_REQUEST, $this->createMock($name)->disableOriginalConstructor()->getMock()),
           ];
         }
       }
@@ -268,16 +276,3 @@ namespace Drupal\Tests\r4032login\Unit {
 
   }
 }
-
-namespace {
-
-  if (!function_exists('drupal_set_message')) {
-
-    /**
-     * Replaces drupal_set_message().
-     */
-    function drupal_set_message() {
-    }
-
-  }
-}