diff --git a/lib/Db/AssignedUsersMapper.php b/lib/Db/AssignedUsersMapper.php
index f7bc5c085..025570055 100644
--- a/lib/Db/AssignedUsersMapper.php
+++ b/lib/Db/AssignedUsersMapper.php
@@ -25,6 +25,7 @@
 
 namespace OCA\Deck\Db;
 
+use OCA\Deck\NotFoundException;
 use OCA\Deck\Service\CirclesService;
 use OCP\AppFramework\Db\Entity;
 use OCP\AppFramework\Db\QBMapper;
@@ -97,7 +98,7 @@ public function findBoardId($cardId) {
 	public function insert(Entity $entity): Entity {
 		$origin = $this->getOrigin($entity);
 		if ($origin === null) {
-			throw new \Exception('No origin found for assignment');
+			throw new NotFoundException('No origin found for assignment');
 		}
 		/** @var AssignedUsers $assignment */
 		$assignment = parent::insert($entity);
diff --git a/tests/integration/database/AssignedUsersMapperTest.php b/tests/integration/database/AssignedUsersMapperTest.php
index 37a709c65..06749117b 100644
--- a/tests/integration/database/AssignedUsersMapperTest.php
+++ b/tests/integration/database/AssignedUsersMapperTest.php
@@ -23,6 +23,7 @@
 
 namespace OCA\Deck\Db;
 
+use OCA\Deck\NotFoundException;
 use OCA\Deck\Service\AssignmentService;
 use OCA\Deck\Service\BoardService;
 use OCA\Deck\Service\StackService;
@@ -165,8 +166,8 @@ public function testInsertInvalidUser() {
 		$assignment->setCardId($this->cards[1]->getId());
 		$assignment->setParticipant('invalid-username');
 		$assignment->setType(AssignedUsers::TYPE_USER);
-		$actual = $this->assignedUsersMapper->insert($assignment);
-		$this->assertNull($actual);
+		$this->expectException(NotFoundException::class);
+		$this->assignedUsersMapper->insert($assignment);
 	}
 
 	/**