diff --git a/migrations/Version20260524121119.php b/migrations/Version20260524121119.php
new file mode 100644
index 0000000..aacbd52
--- /dev/null
+++ b/migrations/Version20260524121119.php
@@ -0,0 +1,30 @@
+<?php
+
+declare(strict_types=1);
+
+namespace DoctrineMigrations;
+
+use Doctrine\DBAL\Schema\Schema;
+use Doctrine\Migrations\AbstractMigration;
+
+final class Version20260524121119 extends AbstractMigration
+{
+    public function getDescription(): string
+    {
+        return 'Add unique constraint for quiz_candidate with deleted_at filter';
+    }
+
+    public function up(Schema $schema): void
+    {
+        // this up() migration is auto-generated, please modify it to your needs
+        $this->addSql('DROP INDEX uniq_ced2ffa291bd8781853cd175');
+        $this->addSql('CREATE UNIQUE INDEX UNIQ_CED2FFA291BD8781853CD175 ON quiz_candidate (candidate_id, quiz_id) WHERE deleted_at IS NULL');
+    }
+
+    public function down(Schema $schema): void
+    {
+        // this down() migration is auto-generated, please modify it to your needs
+        $this->addSql('DROP INDEX UNIQ_CED2FFA291BD8781853CD175');
+        $this->addSql('CREATE UNIQUE INDEX uniq_ced2ffa291bd8781853cd175 ON quiz_candidate (candidate_id, quiz_id)');
+    }
+}
diff --git a/src/Entity/QuizCandidate.php b/src/Entity/QuizCandidate.php
index 652dcfb..bb5b98f 100644
--- a/src/Entity/QuizCandidate.php
+++ b/src/Entity/QuizCandidate.php
@@ -14,7 +14,7 @@ use Tvdt\Repository\QuizCandidateRepository;
 
 #[Gedmo\SoftDeleteable]
 #[ORM\Entity(repositoryClass: QuizCandidateRepository::class)]
-#[ORM\UniqueConstraint(columns: ['candidate_id', 'quiz_id'])]
+#[ORM\UniqueConstraint(columns: ['candidate_id', 'quiz_id'], options: ['where' => 'deleted_at IS NULL'])]
 class QuizCandidate
 {
     use SoftDeleteableEntity;