diff --git a/Models/Task.php b/Models/Task.php
index 1e31aa8..31bce0f 100755
--- a/Models/Task.php
+++ b/Models/Task.php
@@ -406,11 +406,11 @@ class Task implements \JsonSerializable
     }
 
     /**
-     * @return \DateTime
+     * @return \DateTimeImmutable
      *
      * @since 1.0.0
      */
-    public function getCreatedAt() : \DateTimeInterface
+    public function getCreatedAt() : \DateTimeImmutable
     {
         return $this->createdAt;
     }
diff --git a/Models/TaskElement.php b/Models/TaskElement.php
index b1499b5..6b79258 100755
--- a/Models/TaskElement.php
+++ b/Models/TaskElement.php
@@ -152,11 +152,11 @@ class TaskElement implements \JsonSerializable
     }
 
     /**
-     * @return \DateTime
+     * @return \DateTimeImmutable
      *
      * @since 1.0.0
      */
-    public function getCreatedAt() : \DateTimeInterface
+    public function getCreatedAt() : \DateTimeImmutable
     {
         return $this->createdAt;
     }