diff --git a/kifitos.info.yml b/kifitos.info.yml
index 3034018..50a0831 100644
--- a/kifitos.info.yml
+++ b/kifitos.info.yml
@@ -1,6 +1,7 @@
 name: Terms of Service
 type: module
 core: 8.x
+core_version_requirement: ">=8"
 package: Kirjastot.fi
 description: 'Terms of Service agreements'
 dependencies:
diff --git a/src/AgreementConfigInterface.php b/src/AgreementConfigInterface.php
index 3d92c6e..77018d6 100644
--- a/src/AgreementConfigInterface.php
+++ b/src/AgreementConfigInterface.php
@@ -6,8 +6,8 @@
 
 interface AgreementConfigInterface {
 
-  const ROUTE_GUARD = 1;
-  const MESSAGE = 2;
+  public const ROUTE_GUARD = 1;
+  public const MESSAGE = 2;
 
   public function getLabel();
   public function setLabel($label);
diff --git a/src/Entity/Agreement.php b/src/Entity/Agreement.php
index f516aca..8da7eb5 100644
--- a/src/Entity/Agreement.php
+++ b/src/Entity/Agreement.php
@@ -224,6 +224,7 @@ public static function postDelete(EntityStorageInterface $storage, array $entiti
   }
 
   public static function baseFieldDefinitions(EntityTypeInterface $entity_type) {
+    $fields = [];
     $fields['id'] = BaseFieldDefinition::create('integer')
       ->setLabel(t('ID'))
       ->setDescription(t('Agreement ID'))
diff --git a/src/EventSubscriber/KernelSubscriber.php b/src/EventSubscriber/KernelSubscriber.php
index 4b425fe..1b0890b 100644
--- a/src/EventSubscriber/KernelSubscriber.php
+++ b/src/EventSubscriber/KernelSubscriber.php
@@ -2,6 +2,7 @@
 
 namespace Drupal\kifitos\EventSubscriber;
 
+use Symfony\Component\HttpKernel\Event\ControllerEvent;
 use Drupal;
 use Drupal\Component\Render\FormattableMarkup;
 use Drupal\Core\Config\ConfigFactoryInterface;
@@ -13,8 +14,6 @@
 use Drupal\user\UserDataInterface;
 use Symfony\Component\EventDispatcher\EventSubscriberInterface;
 use Symfony\Component\HttpKernel\KernelEvents;
-use Symfony\Component\HttpKernel\Event\GetResponseEvent;
-use Symfony\Component\HttpKernel\Event\FilterControllerEvent;
 use Symfony\Component\HttpFoundation\Request;
 
 class KernelSubscriber implements EventSubscriberInterface {
@@ -37,7 +36,7 @@ public function __construct(ControllerResolverInterface $controller_resolver, Ag
     $this->userData = $user_data;
   }
 
-  public function onController(FilterControllerEvent $event) {
+  public function onController(ControllerEvent $event) {
     $user = Drupal::currentUser();
 
     $controller = $event->getController();
@@ -60,7 +59,7 @@ public function onController(FilterControllerEvent $event) {
 
         case AgreementConfigInterface::MESSAGE:
           if ($event->getRequest()->isMethod('get')) {
-            drupal_set_message(new FormattableMarkup($agreement->getConfig()->getMessage(), []), 'warning', FALSE);
+            \Drupal::messenger()->addWarning(new FormattableMarkup($agreement->getConfig()->getMessage(), []), FALSE);
           }
           break;
       }
diff --git a/src/EventSubscriber/RouteSubscriber.php b/src/EventSubscriber/RouteSubscriber.php
index 0c3bd58..24a6db0 100644
--- a/src/EventSubscriber/RouteSubscriber.php
+++ b/src/EventSubscriber/RouteSubscriber.php
@@ -11,7 +11,7 @@ class RouteSubscriber extends RouteSubscriberBase {
   protected $entityManager;
   protected $configStorage;
 
-  const ROUTE_GUARD = '_kifitos_route_access';
+  public const ROUTE_GUARD = '_kifitos_route_access';
 
   public function __construct(EntityTypeManagerInterface $entity_manager) {
     $this->entityManager = $entity_manager;
@@ -30,7 +30,7 @@ protected function alterRoutes(RouteCollection $collection) {
           $route->setRequirement(self::ROUTE_GUARD, 'TRUE');
           $route->setDefault('_kifitos', $config->id());
         } else {
-          trigger_error(sprintf('%s: Route \'%d\' does not exist.', __CLASS__,  $route_id));
+          trigger_error(sprintf('%s: Route \'%d\' does not exist.', self::class,  $route_id));
         }
       }
     }
diff --git a/src/Form/AgreementApproveForm.php b/src/Form/AgreementApproveForm.php
index ae2acb6..743d820 100644
--- a/src/Form/AgreementApproveForm.php
+++ b/src/Form/AgreementApproveForm.php
@@ -2,10 +2,11 @@
 
 namespace Drupal\kifitos\Form;
 
+use Drupal\Component\Datetime\TimeInterface;
 use Drupal\Core\Cache\Cache;
 use Drupal\Core\Entity\ContentEntityForm;
-use Drupal\Core\Entity\Controller\EntityViewController;
-use Drupal\Core\Entity\EntityManagerInterface;
+use Drupal\Core\Entity\EntityRepositoryInterface;
+use Drupal\Core\Entity\EntityTypeBundleInfoInterface;
 use Drupal\Core\Form\FormStateInterface;
 use Drupal\kifitos\Access\RouteGuard;
 use Drupal\user\UserDataInterface;
@@ -14,18 +15,23 @@
 class AgreementApproveForm extends ContentEntityForm {
   protected $userData;
 
+  public function __construct(EntityRepositoryInterface $entity_repository, EntityTypeBundleInfoInterface $entity_type_bundle_info, TimeInterface $time, UserDataInterface $user_data) {
+    parent::__construct($entity_repository, $entity_type_bundle_info, $time);
+    $this->userData = $user_data;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
   public static function create(ContainerInterface $container) {
     return new static(
-      $container->get('entity.manager'),
+      $container->get('entity.repository'),
+      $container->get('entity_type.bundle.info'),
+      $container->get('datetime.time'),
       $container->get('user.data')
     );
   }
 
-  public function __construct(EntityManagerInterface $entity_manager, UserDataInterface $user_data) {
-    parent::__construct($entity_manager);
-    $this->userData = $user_data;
-  }
-
   public function buildForm(array $form, FormStateInterface $form_state) {
     parent::buildForm($form, $form_state);
 
@@ -52,6 +58,7 @@ public function submitForm(array &$form, FormStateInterface $form_state) {
   }
 
   public function view(array $form, FormStateInterface $form_state) {
+    $view = [];
     $view['body'] = [
       '#type' => 'fieldset',
       '#title' => $this->t('Terms of service'),
diff --git a/src/Form/AgreementConfigForm.php b/src/Form/AgreementConfigForm.php
index ad6fc3e..b55c8f8 100644
--- a/src/Form/AgreementConfigForm.php
+++ b/src/Form/AgreementConfigForm.php
@@ -70,6 +70,6 @@ public function submitForm(array &$form, FormStateInterface $form_state) {
 
   public function save(array $form, FormStateInterface $form_state) {
     $this->entity->save();
-    drupal_set_message($this->t('Configuration updated.'));
+    $this->messenger()->addStatus($this->t('Configuration updated.'));
   }
 }