diff --git a/Models/Group.php b/Models/Group.php
index e248f49..6b4a230 100755
--- a/Models/Group.php
+++ b/Models/Group.php
@@ -73,11 +73,11 @@ class Group extends \phpOMS\Account\Group
     /**
      * Get created at.
      *
-     * @return \DateTime
+     * @return \DateTimeImmutable
      *
      * @since 1.0.0
      */
-    public function getCreatedAt() : \DateTimeInterface
+    public function getCreatedAt() : \DateTimeImmutable
     {
         return $this->createdAt;
     }
diff --git a/Models/Module.php b/Models/Module.php
index d9651a2..386fbc3 100755
--- a/Models/Module.php
+++ b/Models/Module.php
@@ -92,11 +92,11 @@ class Module
     /**
      * Get created at.
      *
-     * @return \DateTime
+     * @return \DateTimeImmutable
      *
      * @since 1.0.0
      */
-    public function getCreatedAt() : \DateTimeInterface
+    public function getCreatedAt() : \DateTimeImmutable
     {
         return $this->createdAt;
     }