diff --git a/Models/QAAnswer.php b/Models/QAAnswer.php
index fa1ba27..86b1f42 100755
--- a/Models/QAAnswer.php
+++ b/Models/QAAnswer.php
@@ -83,7 +83,7 @@ class QAAnswer implements \JsonSerializable
      * @var \DateTime
      * @since 1.0.0
      */
-    private \DateTime $createdAt;
+    private \DateTimeImmutable $createdAt;
 
     /**
      * Constructor.
@@ -92,7 +92,7 @@ class QAAnswer implements \JsonSerializable
      */
     public function __construct()
     {
-        $this->createdAt = new \DateTime('now');
+        $this->createdAt = new \DateTimeImmutable('now');
         $this->createdBy = new NullAccount();
         $this->question  = new NullQAQuestion();
     }
@@ -246,7 +246,7 @@ class QAAnswer implements \JsonSerializable
      *
      * @since 1.0.0
      */
-    public function getCreatedAt() : \DateTime
+    public function getCreatedAt() : \DateTimeInterface
     {
         return $this->createdAt;
     }
diff --git a/Models/QAAnswerMapper.php b/Models/QAAnswerMapper.php
index b2e7812..a472056 100755
--- a/Models/QAAnswerMapper.php
+++ b/Models/QAAnswerMapper.php
@@ -40,7 +40,7 @@ final class QAAnswerMapper extends DataMapperAbstract
         'qa_answer_status'     => ['name' => 'qa_answer_status',     'type' => 'int',      'internal' => 'status'],
         'qa_answer_accepted'   => ['name' => 'qa_answer_accepted',   'type' => 'bool',     'internal' => 'isAccepted'],
         'qa_answer_created_by' => ['name' => 'qa_answer_created_by', 'type' => 'int',      'internal' => 'createdBy', 'readonly' => true],
-        'qa_answer_created_at' => ['name' => 'qa_answer_created_at', 'type' => 'DateTime', 'internal' => 'createdAt', 'readonly' => true],
+        'qa_answer_created_at' => ['name' => 'qa_answer_created_at', 'type' => 'DateTimeImmutable', 'internal' => 'createdAt', 'readonly' => true],
     ];
 
     /**
diff --git a/Models/QAQuestion.php b/Models/QAQuestion.php
index e3b7784..231e6e7 100755
--- a/Models/QAQuestion.php
+++ b/Models/QAQuestion.php
@@ -84,7 +84,7 @@ class QAQuestion implements \JsonSerializable
      * @var \DateTime
      * @since 1.0.0
      */
-    private \DateTime $createdAt;
+    private \DateTimeImmutable $createdAt;
 
     /**
      * Badges.
@@ -109,7 +109,7 @@ class QAQuestion implements \JsonSerializable
      */
     public function __construct()
     {
-        $this->createdAt = new \DateTime('now');
+        $this->createdAt = new \DateTimeImmutable('now');
         $this->createdBy = new NullAccount();
     }
 
@@ -324,7 +324,7 @@ class QAQuestion implements \JsonSerializable
      *
      * @since 1.0.0
      */
-    public function getCreatedAt() : \DateTime
+    public function getCreatedAt() : \DateTimeInterface
     {
         return $this->createdAt;
     }
diff --git a/Models/QAQuestionMapper.php b/Models/QAQuestionMapper.php
index 4d00227..1d9958f 100755
--- a/Models/QAQuestionMapper.php
+++ b/Models/QAQuestionMapper.php
@@ -41,7 +41,7 @@ final class QAQuestionMapper extends DataMapperAbstract
         'qa_question_status'     => ['name' => 'qa_question_status',     'type' => 'int',      'internal' => 'status'],
         'qa_question_category'   => ['name' => 'qa_question_category',   'type' => 'int',      'internal' => 'category'],
         'qa_question_created_by' => ['name' => 'qa_question_created_by', 'type' => 'int',      'internal' => 'createdBy', 'readonly' => true],
-        'qa_question_created_at' => ['name' => 'qa_question_created_at', 'type' => 'DateTime', 'internal' => 'createdAt', 'readonly' => true],
+        'qa_question_created_at' => ['name' => 'qa_question_created_at', 'type' => 'DateTimeImmutable', 'internal' => 'createdAt', 'readonly' => true],
     ];
 
     /**
diff --git a/tests/Models/QAAnswerTest.php b/tests/Models/QAAnswerTest.php
index 416e067..7c9495a 100755
--- a/tests/Models/QAAnswerTest.php
+++ b/tests/Models/QAAnswerTest.php
@@ -34,7 +34,7 @@ class QAAnswerTest extends \PHPUnit\Framework\TestCase
         self::assertFalse($answer->isAccepted());
         self::assertEquals(QAAnswerStatus::ACTIVE, $answer->getStatus());
         self::assertEquals(0, $answer->getCreatedBy()->getId());
-        self::assertInstanceOf('\DateTime', $answer->getCreatedAt());
+        self::assertInstanceOf('\DateTimeImmutable', $answer->getCreatedAt());
     }
 
     public function testSetGet() : void
diff --git a/tests/Models/QAQuestionTest.php b/tests/Models/QAQuestionTest.php
index 563c903..c5d9526 100755
--- a/tests/Models/QAQuestionTest.php
+++ b/tests/Models/QAQuestionTest.php
@@ -35,7 +35,7 @@ class QAQuestionTest extends \PHPUnit\Framework\TestCase
         self::assertEquals(0, $question->getCategory()->getId());
         self::assertEquals('', $question->getLanguage());
         self::assertEquals(0, $question->getCreatedBy()->getId());
-        self::assertInstanceOf('\DateTime', $question->getCreatedAt());
+        self::assertInstanceOf('\DateTimeImmutable', $question->getCreatedAt());
         self::assertEquals([], $question->getBadges());
     }