diff --git a/framework/core/src/Notification/NotificationSyncer.php b/framework/core/src/Notification/NotificationSyncer.php
index 18d845a8d..752538cab 100644
--- a/framework/core/src/Notification/NotificationSyncer.php
+++ b/framework/core/src/Notification/NotificationSyncer.php
@@ -9,6 +9,7 @@
 
 namespace Flarum\Notification;
 
+use Flarum\Database\AbstractModel;
 use Flarum\Notification\Blueprint\BlueprintInterface;
 use Flarum\Notification\Driver\NotificationDriverInterface;
 use Flarum\User\User;
@@ -74,6 +75,12 @@ class NotificationSyncer
                 continue;
             }
 
+            // To add access checking on notification subjects, we first attempt
+            // to load visible subjects to this user.
+            if (! $this->userCanSeeSubject($user, $blueprint->getSubject())) {
+                continue;
+            }
+
             $existing = $toDelete->first(function ($notification) use ($user) {
                 return $notification->user_id === $user->id;
             });
@@ -161,6 +168,18 @@ class NotificationSyncer
         Notification::whereIn('id', $ids)->update(['is_deleted' => $isDeleted]);
     }
 
+    /**
+     * Check access to determine if the recipient is allowed to receive the notification.
+     */
+    protected function userCanSeeSubject(User $user, ?AbstractModel $subject): bool
+    {
+        if ($subject && method_exists($subject, 'registerVisibilityScoper')) {
+            return (bool) $subject->newQuery()->whereVisibleTo($user)->find($subject->id);
+        }
+
+        return true;
+    }
+
     /**
      * Adds a notification driver to the list.
      *
diff --git a/framework/core/tests/integration/notification/NotificationSyncerTest.php b/framework/core/tests/integration/notification/NotificationSyncerTest.php
new file mode 100644
index 000000000..635a93770
--- /dev/null
+++ b/framework/core/tests/integration/notification/NotificationSyncerTest.php
@@ -0,0 +1,169 @@
+<?php
+
+/*
+ * This file is part of Flarum.
+ *
+ * For detailed copyright and license information, please view the
+ * LICENSE file that was distributed with this source code.
+ */
+
+namespace Flarum\Tests\integration\notification;
+
+use Carbon\Carbon;
+use Flarum\Api\Serializer\BasicDiscussionSerializer;
+use Flarum\Api\Serializer\BasicPostSerializer;
+use Flarum\Database\AbstractModel;
+use Flarum\Discussion\Discussion;
+use Flarum\Extend;
+use Flarum\Notification\Blueprint\BlueprintInterface;
+use Flarum\Notification\Notification;
+use Flarum\Notification\NotificationSyncer;
+use Flarum\Post\Post;
+use Flarum\Testing\integration\RetrievesAuthorizedUsers;
+use Flarum\Testing\integration\TestCase;
+use Flarum\User\User;
+
+class NotificationSyncerTest extends TestCase
+{
+    use RetrievesAuthorizedUsers;
+
+    protected function setUp(): void
+    {
+        parent::setUp();
+
+        $this->prepareDatabase([
+            'users' => [
+                $this->normalUser(),
+                ['id' => 3, 'username' => 'Receiver', 'email' => 'receiver@machine.local', 'is_email_confirmed' => 1],
+            ],
+            'discussions' => [
+                ['id' => 1, 'title' => 'Public discussion', 'created_at' => Carbon::parse('2021-11-01 13:00:00')->toDateTimeString(), 'user_id' => 2, 'first_post_id' => 1, 'comment_count' => 2, 'is_private' => 0, 'last_post_number' => 2],
+
+                ['id' => 2, 'title' => 'Private discussion', 'created_at' => Carbon::parse('2021-11-01 13:00:00')->toDateTimeString(), 'user_id' => 2, 'first_post_id' => 3, 'comment_count' => 2, 'is_private' => 1, 'last_post_number' => 2],
+            ],
+            'posts' => [
+                ['id' => 1, 'discussion_id' => 1, 'number' => 1, 'created_at' => Carbon::parse('2021-11-01 13:00:00')->toDateTimeString(), 'user_id' => 2, 'type' => 'comment', 'content' => '<t></t>', 'is_private' => 0],
+                ['id' => 2, 'discussion_id' => 1, 'number' => 2, 'created_at' => Carbon::parse('2021-11-01 13:00:03')->toDateTimeString(), 'user_id' => 2, 'type' => 'comment', 'content' => '<t></t>', 'is_private' => 1],
+
+                ['id' => 3, 'discussion_id' => 2, 'number' => 1, 'created_at' => Carbon::parse('2021-11-01 13:00:00')->toDateTimeString(), 'user_id' => 2, 'type' => 'comment', 'content' => '<t></t>', 'is_private' => 0],
+            ],
+        ]);
+    }
+
+    /**
+     * @dataProvider visibleSubjectsProvider
+     * @param class-string<AbstractModel> $subjectClass
+     * @test
+     */
+    public function can_receive_notification_for_visible_subjects(string $subjectClass, int $subjectId, string $serializer)
+    {
+        $this->expect_notification_count_from_sending_notification_type_with_subject(
+            2,
+            $subjectClass,
+            $subjectId,
+            $serializer
+        );
+    }
+
+
+    /**
+     * @dataProvider invisibleSubjectsProvider
+     * @test
+     */
+    public function cannot_receive_notification_for_restricted_subjects(string $subjectClass, int $subjectId, string $serializer)
+    {
+        $this->expect_notification_count_from_sending_notification_type_with_subject(
+            0,
+            $subjectClass,
+            $subjectId,
+            $serializer
+        );
+    }
+
+    /**
+     * @param class-string<AbstractModel> $subjectClass
+     */
+    protected function expect_notification_count_from_sending_notification_type_with_subject(int $count, string $subjectClass, int $subjectId, string $serializer)
+    {
+        CustomNotificationType::$subjectModel = $subjectClass;
+
+        $this->extend(
+            (new Extend\Notification())
+                ->type(CustomNotificationType::class, $serializer, ['alert'])
+        );
+
+        /** @var NotificationSyncer $syncer */
+        $syncer = $this->app()->getContainer()->make(NotificationSyncer::class);
+
+        $subject = $subjectClass::query()->find($subjectId);
+
+        $syncer->sync(
+            $blueprint = new CustomNotificationType($subject),
+            User::query()
+                ->whereIn('id', [1, 3])
+                ->get()
+                ->all()
+        );
+
+        $this->assertEquals(
+            $count,
+            Notification::query()
+                ->matchingBlueprint($blueprint)
+                ->whereSubject($subject)
+                ->count()
+        );
+    }
+
+    protected function visibleSubjectsProvider()
+    {
+        return [
+            [Post::class, 1, BasicPostSerializer::class],
+            [Discussion::class, 1, BasicDiscussionSerializer::class],
+        ];
+    }
+
+    protected function invisibleSubjectsProvider()
+    {
+        return [
+            [Post::class, 2, BasicPostSerializer::class],
+            [Discussion::class, 2, BasicDiscussionSerializer::class],
+            [Post::class, 3, BasicPostSerializer::class],
+        ];
+    }
+}
+
+class CustomNotificationType implements BlueprintInterface
+{
+    protected $subject;
+    public static $subjectModel;
+
+    public function __construct($subject)
+    {
+        $this->subject = $subject;
+    }
+
+    public function getFromUser()
+    {
+        return null;
+    }
+
+    public function getSubject()
+    {
+        return $this->subject;
+    }
+
+    public function getData()
+    {
+        return [];
+    }
+
+    public static function getType()
+    {
+        return 'customNotificationType';
+    }
+
+    public static function getSubjectModel()
+    {
+        return self::$subjectModel;
+    }
+}