diff --git a/src/Mapper/TaskApiToEntityMapper.php b/src/Mapper/TaskApiToEntityMapper.php
index bc4be6b..a8422ca 100644
--- a/src/Mapper/TaskApiToEntityMapper.php
+++ b/src/Mapper/TaskApiToEntityMapper.php
@@ -64,7 +64,10 @@ class TaskApiToEntityMapper implements MapperInterface
         assert($entity instanceof Task);
         $entity->setHeadline($dto->headline);
         $entity->setDescription($dto->description);
-        $entity->setDueAt($dto->dueAt);
+        $dueAt = $dto->dueAt !== null ?
+            \DateTimeImmutable::createFromFormat('Y-m-d', $dto->dueAt) :
+            null;
+        $entity->setDueAt($dueAt);
         $entity->setPartner(null);
         if ($dto->partner !== null) {
             assert($dto->partner instanceof PartnerApi);