diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 923f2ce49c9..9c46d891719 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -11,7 +11,7 @@ jobs:
         strategy:
             fail-fast: false
             matrix:
-                php-versions: ['7.2', '7.3', '7.4', '8.0', '8.1', '8.2', '8.3']
+                php-versions: ['7.2', '7.3', '7.4', '8.0', '8.1', '8.2', '8.3', '8.4']
 
         steps:
             - uses: actions/checkout@v4
@@ -27,6 +27,8 @@ jobs:
 
             - name: Run phpunit
               run: vendor/bin/phpunit --verbose
+              env:
+                  SYMFONY_DEPRECATIONS_HELPER: 'max[self]=0'
 
     phpstan:
         name: PHPStan
diff --git a/composer.json b/composer.json
index f3d598d6940..c1da1aefbca 100644
--- a/composer.json
+++ b/composer.json
@@ -33,7 +33,7 @@
     },
     "require-dev": {
         "symfony/cache": "^5.1.8",
-        "guzzlehttp/psr7": "^1.7",
+        "guzzlehttp/psr7": "^2.7",
         "http-interop/http-factory-guzzle": "^1.0",
         "guzzlehttp/guzzle": "^7.2",
         "php-http/mock-client": "^1.4.1",
diff --git a/lib/Github/Api/Notification.php b/lib/Github/Api/Notification.php
index e8c9b246a11..f720ad0c88c 100644
--- a/lib/Github/Api/Notification.php
+++ b/lib/Github/Api/Notification.php
@@ -27,7 +27,7 @@ class Notification extends AbstractApi
      *
      * @return array array of notifications
      */
-    public function all($includingRead = false, $participating = false, DateTime $since = null, DateTime $before = null)
+    public function all($includingRead = false, $participating = false, ?DateTime $since = null, ?DateTime $before = null)
     {
         $parameters = [
             'all' => $includingRead,
@@ -54,7 +54,7 @@ public function all($includingRead = false, $participating = false, DateTime $si
      *
      * @param DateTime|null $since
      */
-    public function markRead(DateTime $since = null)
+    public function markRead(?DateTime $since = null)
     {
         $parameters = [];
 
diff --git a/lib/Github/Api/Repository/Actions/Workflows.php b/lib/Github/Api/Repository/Actions/Workflows.php
index e425f9d2651..9a1c9e31c7b 100644
--- a/lib/Github/Api/Repository/Actions/Workflows.php
+++ b/lib/Github/Api/Repository/Actions/Workflows.php
@@ -70,7 +70,7 @@ public function usage(string $username, string $repository, $workflow)
      *
      * @return array|string empty
      */
-    public function dispatches(string $username, string $repository, $workflow, string $ref, array $inputs = null)
+    public function dispatches(string $username, string $repository, $workflow, string $ref, ?array $inputs = null)
     {
         if (is_string($workflow)) {
             $workflow = rawurlencode($workflow);
diff --git a/lib/Github/Api/Repository/Contents.php b/lib/Github/Api/Repository/Contents.php
index b6e170ebce0..a3cc1a3ea0e 100644
--- a/lib/Github/Api/Repository/Contents.php
+++ b/lib/Github/Api/Repository/Contents.php
@@ -98,7 +98,7 @@ public function show($username, $repository, $path = null, $reference = null, $r
      *
      * @return array information about the new file
      */
-    public function create($username, $repository, $path, $content, $message, $branch = null, array $committer = null)
+    public function create($username, $repository, $path, $content, $message, $branch = null, ?array $committer = null)
     {
         $url = '/repos/'.rawurlencode($username).'/'.rawurlencode($repository).'/contents/'.rawurlencode($path);
 
@@ -174,7 +174,7 @@ public function exists($username, $repository, $path, $reference = null)
      *
      * @return array information about the updated file
      */
-    public function update($username, $repository, $path, $content, $message, $sha, $branch = null, array $committer = null)
+    public function update($username, $repository, $path, $content, $message, $sha, $branch = null, ?array $committer = null)
     {
         $url = '/repos/'.rawurlencode($username).'/'.rawurlencode($repository).'/contents/'.rawurlencode($path);
 
@@ -215,7 +215,7 @@ public function update($username, $repository, $path, $content, $message, $sha,
      *
      * @return array information about the updated file
      */
-    public function rm($username, $repository, $path, $message, $sha, $branch = null, array $committer = null)
+    public function rm($username, $repository, $path, $message, $sha, $branch = null, ?array $committer = null)
     {
         $url = '/repos/'.rawurlencode($username).'/'.rawurlencode($repository).'/contents/'.rawurlencode($path);
 
diff --git a/lib/Github/Client.php b/lib/Github/Client.php
index 56d68d59cec..77fcc7b71a2 100644
--- a/lib/Github/Client.php
+++ b/lib/Github/Client.php
@@ -123,7 +123,7 @@ class Client
      * @param string|null  $apiVersion
      * @param string|null  $enterpriseUrl
      */
-    public function __construct(Builder $httpClientBuilder = null, $apiVersion = null, $enterpriseUrl = null)
+    public function __construct(?Builder $httpClientBuilder = null, $apiVersion = null, $enterpriseUrl = null)
     {
         $this->responseHistory = new History();
         $this->httpClientBuilder = $builder = $httpClientBuilder ?? new Builder();
diff --git a/lib/Github/Exception/ApiLimitExceedException.php b/lib/Github/Exception/ApiLimitExceedException.php
index 5c1dd4d8a17..c21f5c2729e 100644
--- a/lib/Github/Exception/ApiLimitExceedException.php
+++ b/lib/Github/Exception/ApiLimitExceedException.php
@@ -20,7 +20,7 @@ class ApiLimitExceedException extends RuntimeException
      * @param int            $code
      * @param Throwable|null $previous
      */
-    public function __construct(int $limit = 5000, int $reset = 1800, int $code = 0, Throwable $previous = null)
+    public function __construct(int $limit = 5000, int $reset = 1800, int $code = 0, ?Throwable $previous = null)
     {
         $this->limit = (int) $limit;
         $this->reset = (int) $reset;
diff --git a/lib/Github/Exception/MissingArgumentException.php b/lib/Github/Exception/MissingArgumentException.php
index 4cd3aeca81d..742cdc5ac7f 100644
--- a/lib/Github/Exception/MissingArgumentException.php
+++ b/lib/Github/Exception/MissingArgumentException.php
@@ -14,7 +14,7 @@ class MissingArgumentException extends ErrorException
      * @param int            $code
      * @param Throwable|null $previous
      */
-    public function __construct($required, int $code = 0, Throwable $previous = null)
+    public function __construct($required, int $code = 0, ?Throwable $previous = null)
     {
         if (is_string($required)) {
             $required = [$required];
diff --git a/lib/Github/Exception/SsoRequiredException.php b/lib/Github/Exception/SsoRequiredException.php
index 1725270a036..09b9d63db08 100644
--- a/lib/Github/Exception/SsoRequiredException.php
+++ b/lib/Github/Exception/SsoRequiredException.php
@@ -14,7 +14,7 @@ class SsoRequiredException extends RuntimeException
      * @param int            $code
      * @param Throwable|null $previous
      */
-    public function __construct(string $url, int $code = 0, Throwable $previous = null)
+    public function __construct(string $url, int $code = 0, ?Throwable $previous = null)
     {
         $this->url = $url;
 
diff --git a/lib/Github/Exception/TwoFactorAuthenticationRequiredException.php b/lib/Github/Exception/TwoFactorAuthenticationRequiredException.php
index c57e67b8e1d..139033dff5b 100644
--- a/lib/Github/Exception/TwoFactorAuthenticationRequiredException.php
+++ b/lib/Github/Exception/TwoFactorAuthenticationRequiredException.php
@@ -14,7 +14,7 @@ class TwoFactorAuthenticationRequiredException extends RuntimeException
      * @param int            $code
      * @param Throwable|null $previous
      */
-    public function __construct(string $type, int $code = 0, Throwable $previous = null)
+    public function __construct(string $type, int $code = 0, ?Throwable $previous = null)
     {
         $this->type = $type;
         parent::__construct('Two factor authentication is enabled on this account', $code, $previous);
diff --git a/lib/Github/HttpClient/Builder.php b/lib/Github/HttpClient/Builder.php
index a8713de13bc..c77f1ac83d8 100644
--- a/lib/Github/HttpClient/Builder.php
+++ b/lib/Github/HttpClient/Builder.php
@@ -78,9 +78,9 @@ class Builder
      * @param StreamFactoryInterface|null  $streamFactory
      */
     public function __construct(
-        ClientInterface $httpClient = null,
-        RequestFactoryInterface $requestFactory = null,
-        StreamFactoryInterface $streamFactory = null
+        ?ClientInterface $httpClient = null,
+        ?RequestFactoryInterface $requestFactory = null,
+        ?StreamFactoryInterface $streamFactory = null
     ) {
         $this->httpClient = $httpClient ?? Psr18ClientDiscovery::find();
         $this->requestFactory = $requestFactory ?? Psr17FactoryDiscovery::findRequestFactory();
diff --git a/lib/Github/ResultPager.php b/lib/Github/ResultPager.php
index a1d94785ca6..4583e5e1268 100644
--- a/lib/Github/ResultPager.php
+++ b/lib/Github/ResultPager.php
@@ -59,7 +59,7 @@ class ResultPager implements ResultPagerInterface
      *
      * @return void
      */
-    public function __construct(Client $client, int $perPage = null)
+    public function __construct(Client $client, ?int $perPage = null)
     {
         if (null !== $perPage && ($perPage < 1 || $perPage > 100)) {
             throw new ValueError(sprintf('%s::__construct(): Argument #2 ($perPage) must be between 1 and 100, or null', self::class));
diff --git a/test/Github/Tests/Api/AbstractApiTest.php b/test/Github/Tests/Api/AbstractApiTest.php
index 428ece12cf3..53e0eb6970a 100644
--- a/test/Github/Tests/Api/AbstractApiTest.php
+++ b/test/Github/Tests/Api/AbstractApiTest.php
@@ -4,6 +4,7 @@
 
 use Github\Api\AbstractApi;
 use GuzzleHttp\Psr7\Response;
+use GuzzleHttp\Psr7\Utils;
 use Http\Client\Common\HttpMethodsClientInterface;
 
 class AbstractApiTest extends TestCase
@@ -232,7 +233,7 @@ private function getPSR7Response($expectedArray)
         return new Response(
             200,
             ['Content-Type' => 'application/json'],
-            \GuzzleHttp\Psr7\stream_for(json_encode($expectedArray))
+            Utils::streamFor(json_encode($expectedArray))
         );
     }
 }
diff --git a/test/Github/Tests/Functional/CacheTest.php b/test/Github/Tests/Functional/CacheTest.php
index eef379e61d5..bd217dc5dc2 100644
--- a/test/Github/Tests/Functional/CacheTest.php
+++ b/test/Github/Tests/Functional/CacheTest.php
@@ -5,6 +5,7 @@
 use Github\AuthMethod;
 use Github\Client;
 use GuzzleHttp\Psr7\Response;
+use GuzzleHttp\Psr7\Utils;
 use Symfony\Component\Cache\Adapter\ArrayAdapter;
 
 /**
@@ -61,7 +62,7 @@ private function getCurrentUserResponse($username)
             'Content-Type' => 'application/json',
         ];
 
-        $body = \GuzzleHttp\Psr7\stream_for(json_encode([
+        $body = Utils::streamFor(json_encode([
             'login' => $username,
         ]));
 
diff --git a/test/Github/Tests/HttpClient/Message/ResponseMediatorTest.php b/test/Github/Tests/HttpClient/Message/ResponseMediatorTest.php
index 5171ab0bac8..b6216d57044 100644
--- a/test/Github/Tests/HttpClient/Message/ResponseMediatorTest.php
+++ b/test/Github/Tests/HttpClient/Message/ResponseMediatorTest.php
@@ -4,6 +4,7 @@
 
 use Github\HttpClient\Message\ResponseMediator;
 use GuzzleHttp\Psr7\Response;
+use GuzzleHttp\Psr7\Utils;
 
 /**
  * @author Tobias Nyholm <tobias.nyholm@gmail.com>
@@ -16,7 +17,7 @@ public function testGetContent()
         $response = new Response(
             200,
             ['Content-Type' => 'application/json'],
-            \GuzzleHttp\Psr7\stream_for(json_encode($body))
+            Utils::streamFor(json_encode($body))
         );
 
         $this->assertEquals($body, ResponseMediator::getContent($response));
@@ -31,7 +32,7 @@ public function testGetContentNotJson()
         $response = new Response(
             200,
             [],
-            \GuzzleHttp\Psr7\stream_for($body)
+            Utils::streamFor($body)
         );
 
         $this->assertEquals($body, ResponseMediator::getContent($response));
@@ -46,7 +47,7 @@ public function testGetContentInvalidJson()
         $response = new Response(
             200,
             ['Content-Type' => 'application/json'],
-            \GuzzleHttp\Psr7\stream_for($body)
+            Utils::streamFor($body)
         );
 
         $this->assertEquals($body, ResponseMediator::getContent($response));
diff --git a/test/Github/Tests/HttpClient/Plugin/GithubExceptionThrowerTest.php b/test/Github/Tests/HttpClient/Plugin/GithubExceptionThrowerTest.php
index b2541ec0942..7cb7dfe33a8 100644
--- a/test/Github/Tests/HttpClient/Plugin/GithubExceptionThrowerTest.php
+++ b/test/Github/Tests/HttpClient/Plugin/GithubExceptionThrowerTest.php
@@ -20,7 +20,7 @@ class GithubExceptionThrowerTest extends TestCase
     /**
      * @dataProvider responseProvider
      */
-    public function testHandleRequest(ResponseInterface $response, ExceptionInterface $exception = null): void
+    public function testHandleRequest(ResponseInterface $response, ?ExceptionInterface $exception = null): void
     {
         $request = new Request('GET', 'https://api.github.com/issues');
 
diff --git a/test/Github/Tests/Mock/PaginatedResponse.php b/test/Github/Tests/Mock/PaginatedResponse.php
index 9d67b9f42be..296adf86457 100644
--- a/test/Github/Tests/Mock/PaginatedResponse.php
+++ b/test/Github/Tests/Mock/PaginatedResponse.php
@@ -3,6 +3,7 @@
 namespace Github\Tests\Mock;
 
 use GuzzleHttp\Psr7\Response;
+use GuzzleHttp\Psr7\Utils;
 
 /**
  * @author Tobias Nyholm <tobias.nyholm@gmail.com>
@@ -18,10 +19,10 @@ public function __construct($loopCount, array $content = [])
         $this->loopCount = $loopCount;
         $this->content = $content;
 
-        parent::__construct(200, ['Content-Type' => 'application/json'], \GuzzleHttp\Psr7\stream_for(json_encode($content)));
+        parent::__construct(200, ['Content-Type' => 'application/json'], Utils::streamFor(json_encode($content)));
     }
 
-    public function getHeader($header)
+    public function getHeader($header): array
     {
         if ($header === 'Link') {
             if ($this->loopCount > 1) {
@@ -38,7 +39,7 @@ public function getHeader($header)
         return parent::getHeader($header);
     }
 
-    public function hasHeader($header)
+    public function hasHeader($header): bool
     {
         if ($header === 'Link') {
             return true;