diff --git a/src/bundle/DependencyInjection/Configuration.php b/src/bundle/DependencyInjection/Configuration.php
index f297cb85..27b3d19a 100644
--- a/src/bundle/DependencyInjection/Configuration.php
+++ b/src/bundle/DependencyInjection/Configuration.php
@@ -42,7 +42,7 @@ public function __construct($rootNodeName)
         $this->rootNodeName = $rootNodeName;
     }
 
-    public function getConfigTreeBuilder()
+    public function getConfigTreeBuilder(): TreeBuilder
     {
         $treeBuilder = new TreeBuilder($this->rootNodeName);
 
diff --git a/src/bundle/DependencyInjection/IbexaSolrExtension.php b/src/bundle/DependencyInjection/IbexaSolrExtension.php
index 8ae24d4d..d06db193 100644
--- a/src/bundle/DependencyInjection/IbexaSolrExtension.php
+++ b/src/bundle/DependencyInjection/IbexaSolrExtension.php
@@ -13,6 +13,7 @@
 use Ibexa\Solr\Gateway\DistributionStrategy\CloudDistributionStrategy;
 use Ibexa\Solr\Gateway\UpdateSerializerInterface;
 use Ibexa\Solr\Handler;
+use Symfony\Component\Config\Definition\ConfigurationInterface;
 use Symfony\Component\Config\FileLocator;
 use Symfony\Component\DependencyInjection\ChildDefinition;
 use Symfony\Component\DependencyInjection\ContainerBuilder;
@@ -91,7 +92,7 @@ class IbexaSolrExtension extends Extension
 
     public const GATEWAY_UPDATE_SERIALIZER_TAG = 'ibexa.solr.gateway.serializer.update';
 
-    public function getAlias()
+    public function getAlias(): string
     {
         return 'ibexa_solr';
     }
@@ -292,7 +293,7 @@ protected function defineEndpoint(ContainerBuilder $container, $alias, $params)
         );
     }
 
-    public function getConfiguration(array $config, ContainerBuilder $container)
+    public function getConfiguration(array $config, ContainerBuilder $container): ?ConfigurationInterface
     {
         return new Configuration($this->getAlias());
     }
diff --git a/src/bundle/IbexaSolrBundle.php b/src/bundle/IbexaSolrBundle.php
index 91fc1a22..bf2c1db3 100644
--- a/src/bundle/IbexaSolrBundle.php
+++ b/src/bundle/IbexaSolrBundle.php
@@ -16,6 +16,7 @@
 use Ibexa\Solr\Container\Compiler\FieldMapperPass;
 use Ibexa\Solr\Container\Compiler\GatewayRegistryPass;
 use Symfony\Component\DependencyInjection\ContainerBuilder;
+use Symfony\Component\DependencyInjection\Extension\ExtensionInterface;
 use Symfony\Component\HttpKernel\Bundle\Bundle;
 
 class IbexaSolrBundle extends Bundle
@@ -37,7 +38,7 @@ public function build(ContainerBuilder $container)
         $container->addCompilerPass(new CoreFilterRegistryPass());
     }
 
-    public function getContainerExtension()
+    public function getContainerExtension(): ?ExtensionInterface
     {
         if (!isset($this->extension)) {
             $this->extension = new IbexaSolrExtension();