diff --git a/Models/Supplier.php b/Models/Supplier.php
index 772da44..9afe478 100644
--- a/Models/Supplier.php
+++ b/Models/Supplier.php
@@ -64,7 +64,7 @@ class Supplier
      */
     public function __construct()
     {
-        $this->createdAt = new \DateTime('now');
+        $this->createdAt = new \DateTimeImmutable('now');
         $this->profile   = new Profile();
     }
 
@@ -247,7 +247,7 @@ class Supplier
      *
      * @since 1.0.0
      */
-    public function getCreatedAt() : \DateTime
+    public function getCreatedAt() : \DateTimeInterface
     {
         return $this->createdAt;
     }
diff --git a/Models/SupplierMapper.php b/Models/SupplierMapper.php
index 4af88e3..c6ffafc 100644
--- a/Models/SupplierMapper.php
+++ b/Models/SupplierMapper.php
@@ -44,7 +44,7 @@ final class SupplierMapper extends DataMapperAbstract
         'suppliermgmt_supplier_type'       => ['name' => 'suppliermgmt_supplier_type',       'type' => 'int',      'internal' => 'type'],
         'suppliermgmt_supplier_taxid'      => ['name' => 'suppliermgmt_supplier_taxid',      'type' => 'int',      'internal' => 'taxId'],
         'suppliermgmt_supplier_info'       => ['name' => 'suppliermgmt_supplier_info',       'type' => 'string',   'internal' => 'info'],
-        'suppliermgmt_supplier_created_at' => ['name' => 'suppliermgmt_supplier_created_at', 'type' => 'DateTime', 'internal' => 'createdAt', 'readonly' => true],
+        'suppliermgmt_supplier_created_at' => ['name' => 'suppliermgmt_supplier_created_at', 'type' => 'DateTimeImmutable', 'internal' => 'createdAt', 'readonly' => true],
         'suppliermgmt_supplier_account'    => ['name' => 'suppliermgmt_supplier_account',    'type' => 'int',      'internal' => 'profile'],
     ];