diff --git a/src/bundle/Command/GeneratePlatformSchemaCommand.php b/src/bundle/Command/GeneratePlatformSchemaCommand.php
index 8e786e7..2c16c3b 100644
--- a/src/bundle/Command/GeneratePlatformSchemaCommand.php
+++ b/src/bundle/Command/GeneratePlatformSchemaCommand.php
@@ -89,7 +89,7 @@ protected function execute(InputInterface $input, OutputInterface $output): int
         $output->writeln('');
         $this->compileTypes($output);
 
-        return 0;
+        return Command::SUCCESS;
     }
 
     private function compileTypes(OutputInterface $output)
diff --git a/src/bundle/DependencyInjection/Configuration.php b/src/bundle/DependencyInjection/Configuration.php
index 5998040..31b29c1 100644
--- a/src/bundle/DependencyInjection/Configuration.php
+++ b/src/bundle/DependencyInjection/Configuration.php
@@ -20,7 +20,7 @@ class Configuration implements ConfigurationInterface
     /**
      * {@inheritdoc}
      */
-    public function getConfigTreeBuilder()
+    public function getConfigTreeBuilder(): TreeBuilder
     {
         return new TreeBuilder(IbexaGraphQLExtension::EXTENSION_NAME);
     }
diff --git a/src/bundle/IbexaGraphQLBundle.php b/src/bundle/IbexaGraphQLBundle.php
index 12a8e2a..d3dda40 100644
--- a/src/bundle/IbexaGraphQLBundle.php
+++ b/src/bundle/IbexaGraphQLBundle.php
@@ -10,6 +10,7 @@
 use Ibexa\Bundle\GraphQL\DependencyInjection\Compiler;
 use Ibexa\Bundle\GraphQL\DependencyInjection\IbexaGraphQLExtension;
 use Symfony\Component\DependencyInjection\ContainerBuilder;
+use Symfony\Component\DependencyInjection\Extension\ExtensionInterface;
 use Symfony\Component\HttpKernel\Bundle\Bundle;
 
 class IbexaGraphQLBundle extends Bundle
@@ -24,7 +25,7 @@ public function build(ContainerBuilder $container)
         $container->addCompilerPass(new Compiler\SchemaDomainIteratorsPass());
     }
 
-    public function getContainerExtension()
+    public function getContainerExtension(): ?ExtensionInterface
     {
         return new IbexaGraphQLExtension();
     }
diff --git a/src/lib/Value/ContentFieldValue.php b/src/lib/Value/ContentFieldValue.php
index 50f9317..77fb146 100644
--- a/src/lib/Value/ContentFieldValue.php
+++ b/src/lib/Value/ContentFieldValue.php
@@ -50,7 +50,7 @@ public function __get($property)
         return parent::__get($property);
     }
 
-    public function __toString()
+    public function __toString(): string
     {
         return (string)$this->value;
     }
diff --git a/src/lib/Value/Field.php b/src/lib/Value/Field.php
index 0095bc9..f7d771e 100644
--- a/src/lib/Value/Field.php
+++ b/src/lib/Value/Field.php
@@ -23,7 +23,7 @@ public function __get($property)
         return parent::__get($property);
     }
 
-    public function __toString()
+    public function __toString(): string
     {
         return (string)$this->value;
     }