diff --git a/src/DataFixtures/AppFixtures.php b/src/DataFixtures/AppFixtures.php
index 319df2530..f1a1e1251 100644
--- a/src/DataFixtures/AppFixtures.php
+++ b/src/DataFixtures/AppFixtures.php
@@ -85,7 +85,7 @@ private function loadPosts(ObjectManager $manager): void
                 $comment = new Comment();
                 $comment->setAuthor($commentAuthor);
                 $comment->setContent($this->getRandomText(random_int(255, 512)));
-                $comment->setPublishedAt(new \DateTime('now + '.$i.'seconds'));
+                $comment->setPublishedAt(new \DateTimeImmutable('now + '.$i.'seconds'));
 
                 $post->addComment($comment);
             }
@@ -130,7 +130,7 @@ private function getTagData(): array
     /**
      * @throws \Exception
      *
-     * @return array<int, array{0: string, 1: AbstractUnicodeString, 2: string, 3: string, 4: \DateTime, 5: User, 6: array<Tag>}>
+     * @return array<int, array{0: string, 1: AbstractUnicodeString, 2: string, 3: string, 4: \DateTimeImmutable, 5: User, 6: array<Tag>}>
      */
     private function getPostData(): array
     {
@@ -147,7 +147,7 @@ private function getPostData(): array
                 $this->slugger->slug($title)->lower(),
                 $this->getRandomText(),
                 $this->getPostContent(),
-                (new \DateTime('now - '.$i.'days'))->setTime(random_int(8, 17), random_int(7, 49), random_int(0, 59)),
+                (new \DateTimeImmutable('now - '.$i.'days'))->setTime(random_int(8, 17), random_int(7, 49), random_int(0, 59)),
                 // Ensure that the first post is written by Jane Doe to simplify tests
                 $user,
                 $this->getRandomTags(),
diff --git a/src/Entity/Comment.php b/src/Entity/Comment.php
index aa1b8e6bc..707601781 100644
--- a/src/Entity/Comment.php
+++ b/src/Entity/Comment.php
@@ -44,8 +44,8 @@ class Comment
     #[Assert\Length(min: 5, minMessage: 'comment.too_short', max: 10000, maxMessage: 'comment.too_long')]
     private ?string $content = null;
 
-    #[ORM\Column(type: Types::DATETIME_MUTABLE)]
-    private \DateTime $publishedAt;
+    #[ORM\Column]
+    private \DateTimeImmutable $publishedAt;
 
     #[ORM\ManyToOne(targetEntity: User::class)]
     #[ORM\JoinColumn(nullable: false)]
@@ -53,7 +53,7 @@ class Comment
 
     public function __construct()
     {
-        $this->publishedAt = new \DateTime();
+        $this->publishedAt = new \DateTimeImmutable();
     }
 
     #[Assert\IsTrue(message: 'comment.is_spam')]
@@ -79,12 +79,12 @@ public function setContent(string $content): void
         $this->content = $content;
     }
 
-    public function getPublishedAt(): \DateTime
+    public function getPublishedAt(): \DateTimeImmutable
     {
         return $this->publishedAt;
     }
 
-    public function setPublishedAt(\DateTime $publishedAt): void
+    public function setPublishedAt(\DateTimeImmutable $publishedAt): void
     {
         $this->publishedAt = $publishedAt;
     }
diff --git a/src/Entity/Post.php b/src/Entity/Post.php
index 4682e9825..e26524d81 100644
--- a/src/Entity/Post.php
+++ b/src/Entity/Post.php
@@ -58,8 +58,8 @@ class Post
     #[Assert\Length(min: 10, minMessage: 'post.too_short_content')]
     private ?string $content = null;
 
-    #[ORM\Column(type: Types::DATETIME_MUTABLE)]
-    private \DateTime $publishedAt;
+    #[ORM\Column]
+    private \DateTimeImmutable $publishedAt;
 
     #[ORM\ManyToOne(targetEntity: User::class)]
     #[ORM\JoinColumn(nullable: false)]
@@ -83,7 +83,7 @@ class Post
 
     public function __construct()
     {
-        $this->publishedAt = new \DateTime();
+        $this->publishedAt = new \DateTimeImmutable();
         $this->comments = new ArrayCollection();
         $this->tags = new ArrayCollection();
     }
@@ -123,12 +123,12 @@ public function setContent(?string $content): void
         $this->content = $content;
     }
 
-    public function getPublishedAt(): \DateTime
+    public function getPublishedAt(): \DateTimeImmutable
     {
         return $this->publishedAt;
     }
 
-    public function setPublishedAt(\DateTime $publishedAt): void
+    public function setPublishedAt(\DateTimeImmutable $publishedAt): void
     {
         $this->publishedAt = $publishedAt;
     }
diff --git a/src/Form/Type/DateTimePickerType.php b/src/Form/Type/DateTimePickerType.php
index 2400ec1eb..7dddd8182 100644
--- a/src/Form/Type/DateTimePickerType.php
+++ b/src/Form/Type/DateTimePickerType.php
@@ -31,6 +31,7 @@ public function configureOptions(OptionsResolver $resolver): void
         // @see https://symfony.com/doc/current/reference/forms/types/date.html#rendering-a-single-html5-text-box
         $resolver->setDefaults([
             'widget' => 'single_text',
+            'input' => 'datetime_immutable',
             // if true, the browser will display the native date picker widget
             // however, this app uses a custom JavaScript widget, so it must be set to false
             'html5' => false,
diff --git a/src/Repository/PostRepository.php b/src/Repository/PostRepository.php
index 62b026cda..bef34dafc 100644
--- a/src/Repository/PostRepository.php
+++ b/src/Repository/PostRepository.php
@@ -47,7 +47,7 @@ public function findLatest(int $page = 1, ?Tag $tag = null): Paginator
             ->leftJoin('p.tags', 't')
             ->where('p.publishedAt <= :now')
             ->orderBy('p.publishedAt', 'DESC')
-            ->setParameter('now', new \DateTime())
+            ->setParameter('now', new \DateTimeImmutable())
         ;
 
         if (null !== $tag) {