diff --git a/src/Mapper/ContactApiToEntityMapper.php b/src/Mapper/ContactApiToEntityMapper.php
index 931cef0..7129a65 100644
--- a/src/Mapper/ContactApiToEntityMapper.php
+++ b/src/Mapper/ContactApiToEntityMapper.php
@@ -57,7 +57,10 @@ class ContactApiToEntityMapper implements MapperInterface
 
         $entity->setFirstName($dto->firstName);
         $entity->setLastName($dto->lastName);
-        $entity->setBirthday($dto->birthday);
+        $birthDay = $dto->birthday !== null ?
+            \DateTimeImmutable::createFromFormat('Y-m-d', $dto->birthday) :
+            null;
+        $entity->setBirthday($birthDay);
         $entity->setImage($dto->image);
         $entity->setPosition($dto->position);
         $entity->setPhone($dto->phone);