diff --git a/Models/Client.php b/Models/Client.php
index c0568a3..23b5ed9 100644
--- a/Models/Client.php
+++ b/Models/Client.php
@@ -41,7 +41,7 @@ class Client
 
     private string $info = '';
 
-    private \DateTime $createdAt;
+    private \DateTimeImmutable $createdAt;
 
     private Profile $profile;
 
@@ -68,7 +68,7 @@ class Client
      */
     public function __construct()
     {
-        $this->createdAt = new \DateTime('now');
+        $this->createdAt = new \DateTimeImmutable('now');
         $this->profile   = new Profile();
     }
 
@@ -303,7 +303,7 @@ class Client
      *
      * @since 1.0.0
      */
-    public function getCreatedAt() : \DateTime
+    public function getCreatedAt() : \DateTimeInterface
     {
         return $this->createdAt;
     }
diff --git a/Models/ClientMapper.php b/Models/ClientMapper.php
index 2ae971e..e3824ce 100644
--- a/Models/ClientMapper.php
+++ b/Models/ClientMapper.php
@@ -42,7 +42,7 @@ final class ClientMapper extends DataMapperAbstract
         'clientmgmt_client_status'     => ['name' => 'clientmgmt_client_status',     'type' => 'int',      'internal' => 'status'],
         'clientmgmt_client_type'       => ['name' => 'clientmgmt_client_type',       'type' => 'int',      'internal' => 'type'],
         'clientmgmt_client_info'       => ['name' => 'clientmgmt_client_info',       'type' => 'string',   'internal' => 'info'],
-        'clientmgmt_client_created_at' => ['name' => 'clientmgmt_client_created_at', 'type' => 'DateTime', 'internal' => 'createdAt', 'readonly' => true],
+        'clientmgmt_client_created_at' => ['name' => 'clientmgmt_client_created_at', 'type' => 'DateTimeImmutable', 'internal' => 'createdAt', 'readonly' => true],
         'clientmgmt_client_profile'    => ['name' => 'clientmgmt_client_profile',    'type' => 'int',      'internal' => 'profile'],
     ];