diff --git a/.php-cs-fixer.dist.php b/.php-cs-fixer.dist.php
index 800bad1a..48dee738 100644
--- a/.php-cs-fixer.dist.php
+++ b/.php-cs-fixer.dist.php
@@ -5,6 +5,7 @@
     ->setRules([
         '@PHP71Migration:risky' => true,
         '@PHPUnit75Migration:risky' => true,
+        '@PSR12:risky' => true,
         '@Symfony' => true,
         'declare_strict_types' => false,
         'global_namespace_import' => false,
diff --git a/src/GuzzleClient.php b/src/GuzzleClient.php
index 168c88fa..b935480c 100644
--- a/src/GuzzleClient.php
+++ b/src/GuzzleClient.php
@@ -41,9 +41,9 @@ class GuzzleClient extends ServiceClient
     public function __construct(
         ClientInterface $client,
         DescriptionInterface $description,
-        callable $commandToRequestTransformer = null,
-        callable $responseToResultTransformer = null,
-        HandlerStack $commandHandlerStack = null,
+        ?callable $commandToRequestTransformer = null,
+        ?callable $responseToResultTransformer = null,
+        ?HandlerStack $commandHandlerStack = null,
         array $config = []
     ) {
         $this->config = $config;
@@ -96,7 +96,7 @@ public function getDescription()
      *
      * @param callable|null $commandToRequestTransformer
      *
-     * @return \GuzzleHttp\Command\Guzzle\Serializer
+     * @return Serializer
      */
     private function getSerializer($commandToRequestTransformer)
     {
@@ -110,7 +110,7 @@ private function getSerializer($commandToRequestTransformer)
      *
      * @param callable|null $responseToResultTransformer
      *
-     * @return \GuzzleHttp\Command\Guzzle\Deserializer
+     * @return Deserializer
      */
     private function getDeserializer($responseToResultTransformer)
     {
diff --git a/src/Handler/ValidatedDescriptionHandler.php b/src/Handler/ValidatedDescriptionHandler.php
index 49b4dc95..9289eeca 100644
--- a/src/Handler/ValidatedDescriptionHandler.php
+++ b/src/Handler/ValidatedDescriptionHandler.php
@@ -23,7 +23,7 @@ class ValidatedDescriptionHandler
     /**
      * ValidatedDescriptionHandler constructor.
      */
-    public function __construct(DescriptionInterface $description, SchemaValidator $schemaValidator = null)
+    public function __construct(DescriptionInterface $description, ?SchemaValidator $schemaValidator = null)
     {
         $this->description = $description;
         $this->validator = $schemaValidator ?: new SchemaValidator();
diff --git a/src/Operation.php b/src/Operation.php
index 0fbaa217..cca755b4 100644
--- a/src/Operation.php
+++ b/src/Operation.php
@@ -51,7 +51,7 @@ class Operation implements ToArrayInterface
      *
      * @throws \InvalidArgumentException
      */
-    public function __construct(array $config = [], DescriptionInterface $description = null)
+    public function __construct(array $config = [], ?DescriptionInterface $description = null)
     {
         static $defaults = [
             'name' => '',
diff --git a/src/RequestLocation/QueryLocation.php b/src/RequestLocation/QueryLocation.php
index 9e9e090b..53cdb060 100644
--- a/src/RequestLocation/QueryLocation.php
+++ b/src/RequestLocation/QueryLocation.php
@@ -25,7 +25,7 @@ class QueryLocation extends AbstractLocation
      *
      * @param string $locationName
      */
-    public function __construct($locationName = 'query', QuerySerializerInterface $querySerializer = null)
+    public function __construct($locationName = 'query', ?QuerySerializerInterface $querySerializer = null)
     {
         parent::__construct($locationName);
 
diff --git a/src/ResponseLocation/JsonLocation.php b/src/ResponseLocation/JsonLocation.php
index 126ee469..ae1c8e0a 100644
--- a/src/ResponseLocation/JsonLocation.php
+++ b/src/ResponseLocation/JsonLocation.php
@@ -26,7 +26,7 @@ public function __construct($locationName = 'json')
     }
 
     /**
-     * @return \GuzzleHttp\Command\ResultInterface
+     * @return ResultInterface
      */
     public function before(
         ResultInterface $result,
diff --git a/src/Serializer.php b/src/Serializer.php
index d9090118..f3dc8f21 100644
--- a/src/Serializer.php
+++ b/src/Serializer.php
@@ -132,7 +132,7 @@ protected function createRequest(CommandInterface $command)
     /**
      * Create a request for an operation with a uri merged onto a base URI
      *
-     * @return \GuzzleHttp\Psr7\Request
+     * @return Request
      */
     private function createCommandWithUri(
         Operation $operation,
diff --git a/tests/GuzzleClientTest.php b/tests/GuzzleClientTest.php
index 8d315e74..a2595627 100644
--- a/tests/GuzzleClientTest.php
+++ b/tests/GuzzleClientTest.php
@@ -716,8 +716,8 @@ public function testReturnsProcessedResponse()
 
     private function getServiceClient(
         array $responses,
-        MockHandler $mock = null,
-        callable $commandToRequestTransformer = null
+        ?MockHandler $mock = null,
+        ?callable $commandToRequestTransformer = null
     ) {
         $mock = $mock ?: new MockHandler();
 
@@ -954,31 +954,31 @@ public function testDocumentationExampleFromReadme()
         $client = new HttpClient();
         $description = new Description([
             'baseUrl' => 'http://httpbin.org/',
-                'operations' => [
-                    'testing' => [
-                        'httpMethod' => 'GET',
-                        'uri' => '/get{?foo}',
-                        'responseModel' => 'getResponse',
-                        'parameters' => [
-                            'foo' => [
-                                'type' => 'string',
-                                'location' => 'uri',
-                            ],
-                            'bar' => [
-                                'type' => 'string',
-                                'location' => 'query',
-                            ],
+            'operations' => [
+                'testing' => [
+                    'httpMethod' => 'GET',
+                    'uri' => '/get{?foo}',
+                    'responseModel' => 'getResponse',
+                    'parameters' => [
+                        'foo' => [
+                            'type' => 'string',
+                            'location' => 'uri',
+                        ],
+                        'bar' => [
+                            'type' => 'string',
+                            'location' => 'query',
                         ],
                     ],
                 ],
-                'models' => [
-                    'getResponse' => [
-                        'type' => 'object',
-                        'additionalProperties' => [
-                            'location' => 'json',
-                        ],
+            ],
+            'models' => [
+                'getResponse' => [
+                    'type' => 'object',
+                    'additionalProperties' => [
+                        'location' => 'json',
                     ],
                 ],
+            ],
         ]);
 
         $guzzle = new GuzzleClient($client, $description);
@@ -991,39 +991,39 @@ public function testDescriptionWithExtends()
     {
         $client = new HttpClient();
         $description = new Description([
-                'baseUrl' => 'http://httpbin.org/',
-                'operations' => [
-                    'testing' => [
-                        'httpMethod' => 'GET',
-                        'uri' => '/get',
-                        'responseModel' => 'getResponse',
-                        'parameters' => [
-                            'foo' => [
-                                'type' => 'string',
-                                'default' => 'foo',
-                                'location' => 'query',
-                            ],
+            'baseUrl' => 'http://httpbin.org/',
+            'operations' => [
+                'testing' => [
+                    'httpMethod' => 'GET',
+                    'uri' => '/get',
+                    'responseModel' => 'getResponse',
+                    'parameters' => [
+                        'foo' => [
+                            'type' => 'string',
+                            'default' => 'foo',
+                            'location' => 'query',
                         ],
                     ],
-                    'testing_extends' => [
-                        'extends' => 'testing',
-                        'responseModel' => 'getResponse',
-                        'parameters' => [
-                            'bar' => [
-                                'type' => 'string',
-                                'location' => 'query',
-                            ],
+                ],
+                'testing_extends' => [
+                    'extends' => 'testing',
+                    'responseModel' => 'getResponse',
+                    'parameters' => [
+                        'bar' => [
+                            'type' => 'string',
+                            'location' => 'query',
                         ],
                     ],
                 ],
-                'models' => [
-                    'getResponse' => [
-                        'type' => 'object',
-                        'additionalProperties' => [
-                            'location' => 'json',
-                        ],
+            ],
+            'models' => [
+                'getResponse' => [
+                    'type' => 'object',
+                    'additionalProperties' => [
+                        'location' => 'json',
                     ],
                 ],
+            ],
         ]);
         $guzzle = new GuzzleClient($client, $description);
         $result = $guzzle->testing_extends(['bar' => 'bar']);
diff --git a/vendor-bin/php-cs-fixer/composer.json b/vendor-bin/php-cs-fixer/composer.json
index 3e8c9dfb..049eacf1 100644
--- a/vendor-bin/php-cs-fixer/composer.json
+++ b/vendor-bin/php-cs-fixer/composer.json
@@ -1,7 +1,7 @@
 {
     "require": {
         "php": "^7.4 || ^8.0",
-        "friendsofphp/php-cs-fixer": "3.40.2"
+        "friendsofphp/php-cs-fixer": "3.52.1"
     },
     "config": {
         "preferred-install": "dist"