diff --git a/backend/tests/Feature/Element/EloquentElementRepositoryTest.php b/backend/tests/Feature/Element/EloquentElementRepositoryTest.php
index edddeac..c339903 100644
--- a/backend/tests/Feature/Element/EloquentElementRepositoryTest.php
+++ b/backend/tests/Feature/Element/EloquentElementRepositoryTest.php
@@ -10,6 +10,7 @@ use App\Set\SetRepository;
 use App\Shared\ValueObject\EmailAddress;
 use App\User\CreateUserDto;
 use App\User\UserRepository;
+use DomainException;
 use Illuminate\Foundation\Testing\RefreshDatabase;
 use Tests\TestCase;
 
@@ -71,6 +72,31 @@ class EloquentElementRepositoryTest extends TestCase
         );
     }
 
+    public function testItRejectsAParentFromAnotherSet(): void
+    {
+        $bible = $this->createSet('Bible');
+        $course = $this->createSet('Course');
+        $repository = app(ElementRepository::class);
+        $book = $repository->create(new CreateElementDto(
+            set: $bible,
+            name: 'Genesis',
+            kind: 'book',
+            parentElement: null,
+        ));
+
+        $this->expectException(DomainException::class);
+        $this->expectExceptionMessage(
+            'parent element must belong to the same set',
+        );
+
+        $repository->create(new CreateElementDto(
+            set: $course,
+            name: 'Invalid lesson',
+            kind: 'lesson',
+            parentElement: $book,
+        ));
+    }
+
     private function createSet(string $name): Set
     {
         $creator = app(UserRepository::class)->create(new CreateUserDto(