diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index 7fa0ea1..420cb9b 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -39,6 +39,8 @@ jobs:
           - "8.0"
           - "8.1"
           - "8.2"
+          - "8.3"
+          - "8.4"
 
     steps:
       - name: Checkout.
diff --git a/.github/workflows/static.yml b/.github/workflows/static.yml
index 3e79b31..0d90f64 100644
--- a/.github/workflows/static.yml
+++ b/.github/workflows/static.yml
@@ -35,6 +35,7 @@ jobs:
           - "8.0"
           - "8.1"
           - "8.2"
+          - "8.3"
 
     steps:
       - name: Checkout.
diff --git a/src/Infrastructure/Http/WhoopsErrorResponseGenerator.php b/src/Infrastructure/Http/WhoopsErrorResponseGenerator.php
index 3b0e212..30a8517 100644
--- a/src/Infrastructure/Http/WhoopsErrorResponseGenerator.php
+++ b/src/Infrastructure/Http/WhoopsErrorResponseGenerator.php
@@ -30,7 +30,7 @@ final class WhoopsErrorResponseGenerator implements ErrorResponseGeneratorInterf
     /**
      * @param RunInterface|null $whoops
      */
-    public function __construct(RunInterface $whoops = null)
+    public function __construct(?RunInterface $whoops = null)
     {
         if ($whoops instanceof RunInterface) {
             $this->whoops = $whoops;
diff --git a/src/Model/Post/PostRepository.php b/src/Model/Post/PostRepository.php
index 55c7436..7a61644 100644
--- a/src/Model/Post/PostRepository.php
+++ b/src/Model/Post/PostRepository.php
@@ -18,7 +18,7 @@ final class PostRepository
     /**
      * @param array<int, Post>|null $posts
      */
-    public function __construct(array $posts = null)
+    public function __construct(?array $posts = null)
     {
         $this->posts = $posts ?? [
             1 => new Post(1, 'Post #1', new DateTimeImmutable('+1 day')),