diff --git a/bin/graphql-client b/bin/graphql-client
index 22f1da4..69f3c60 100755
--- a/bin/graphql-client
+++ b/bin/graphql-client
@@ -15,7 +15,16 @@ use Symfony\Component\Console\Application;
 
 $application = new Application();
 
-$application->add(new GenerateConfig());
-$application->add(new GetIntrospection());
+if (method_exists($application, 'add')) {
+  // Symfony Console ^6
+  $application->add(new GenerateConfig());
+  $application->add(new GetIntrospection());
+}
+
+if (method_exists($application, 'addCommand')) {
+  // Symfony Console ^7 and above
+  $application->addCommand(new GenerateConfig());
+  $application->addCommand(new GetIntrospection());
+}
 
 $application->run();
diff --git a/composer.json b/composer.json
index 8dab5f2..85cdd52 100644
--- a/composer.json
+++ b/composer.json
@@ -18,7 +18,7 @@
     "guzzlehttp/guzzle": "^6.3 || ^7.0",
     "softonic/guzzle-oauth2-middleware": "^2.1",
     "ext-json": "*",
-    "symfony/console": "^6.0 || ^7.0"
+    "symfony/console": "^6.0 || ^7.0 || ^8.0"
   },
   "require-dev": {
     "friendsofphp/php-cs-fixer": "^3.9",
diff --git a/src/Config/MutationTypeConfig.php b/src/Config/MutationTypeConfig.php
index 9c65203..2befa70 100644
--- a/src/Config/MutationTypeConfig.php
+++ b/src/Config/MutationTypeConfig.php
@@ -23,7 +23,7 @@ class MutationTypeConfig
      */
     public $children = [];
 
-    public function __get(string $propertyName)
+    public function __get(string $propertyName): mixed
     {
         if (property_exists(static::class, $propertyName)) {
             return $this->{$propertyName};
diff --git a/src/Console/Mutation/GenerateConfig.php b/src/Console/Mutation/GenerateConfig.php
index 69f36ed..8badff1 100644
--- a/src/Console/Mutation/GenerateConfig.php
+++ b/src/Console/Mutation/GenerateConfig.php
@@ -28,7 +28,7 @@ class GenerateConfig extends Command
      */
     private $fromSameMutation;
 
-    protected function configure()
+    protected function configure(): void
     {
         $this->setDescription('Creates a mutation config.')
             ->setHelp(
diff --git a/src/Console/Mutation/GetIntrospection.php b/src/Console/Mutation/GetIntrospection.php
index a4dd1d6..4438308 100644
--- a/src/Console/Mutation/GetIntrospection.php
+++ b/src/Console/Mutation/GetIntrospection.php
@@ -10,7 +10,7 @@ class GetIntrospection extends Command
 {
     protected static $defaultName = 'mutation:introspection';
 
-    protected function configure()
+    protected function configure(): void
     {
         $this->setDescription('Returns a instrospection query.')
             ->setHelp('Returns the introspection query needed to execute in your GraphQL server in order ' .
diff --git a/src/DataObjects/AbstractItem.php b/src/DataObjects/AbstractItem.php
index 7242a4e..0ef46ea 100644
--- a/src/DataObjects/AbstractItem.php
+++ b/src/DataObjects/AbstractItem.php
@@ -34,12 +34,12 @@ public function has(string $key): bool
         return $this->arguments[$firstKey]->has($nextKey);
     }
 
-    public function __get(string $key)
+    public function __get(string $key): mixed
     {
         return $this->arguments[$key] ?? null;
     }
 
-    public function __set(string $key, $value): void
+    public function __set(string $key, mixed $value): void
     {
         $this->arguments[$key] = $value;
     }
diff --git a/src/DataObjects/Mutation/Collection.php b/src/DataObjects/Mutation/Collection.php
index 9c5ce8d..e5ea3af 100644
--- a/src/DataObjects/Mutation/Collection.php
+++ b/src/DataObjects/Mutation/Collection.php
@@ -21,7 +21,7 @@ public function add(array $itemData): MutationObject
         return $item;
     }
 
-    public function __unset($key): void
+    public function __unset(string $key): void
     {
         foreach ($this->arguments as $argument) {
             unset($argument->{$key});
diff --git a/src/DataObjects/Mutation/Item.php b/src/DataObjects/Mutation/Item.php
index a01c94a..ca7436e 100644
--- a/src/DataObjects/Mutation/Item.php
+++ b/src/DataObjects/Mutation/Item.php
@@ -20,7 +20,7 @@ public function __construct(array $arguments = [], protected array $config = [],
         $this->hasChanged = $hasChanged;
     }
 
-    public function __get(string $key)
+    public function __get(string $key): mixed
     {
         if ((!array_key_exists($key, $this->arguments) || ($this->arguments[$key] === null))
             && array_key_exists($key, $this->config)
@@ -34,7 +34,7 @@ public function __get(string $key)
         return parent::__get($key);
     }
 
-    public function __set(string $key, $value): void
+    public function __set(string $key, mixed $value): void
     {
         if (!array_key_exists($key, $this->arguments) || $this->arguments[$key] !== $value) {
             $this->hasChanged = true;