diff --git a/Debug/DataCollector.php b/Debug/DataCollector.php
index ab6ab577..ab953782 100644
--- a/Debug/DataCollector.php
+++ b/Debug/DataCollector.php
@@ -42,7 +42,7 @@ public function __construct(
         $this->reset();
     }
 
-    public function collect(Request $request, Response $response, \Throwable $exception = null)
+    public function collect(Request $request, Response $response, \Throwable $exception = null): void
     {
     }
 
diff --git a/DependencyInjection/Compiler/AdjustDecorationPass.php b/DependencyInjection/Compiler/AdjustDecorationPass.php
index 16f5e369..9d63153b 100644
--- a/DependencyInjection/Compiler/AdjustDecorationPass.php
+++ b/DependencyInjection/Compiler/AdjustDecorationPass.php
@@ -21,7 +21,7 @@
  */
 final class AdjustDecorationPass implements CompilerPassInterface
 {
-    public function process(ContainerBuilder $container)
+    public function process(ContainerBuilder $container): void
     {
         DIUtils::adjustDecorators($container);
     }
diff --git a/DependencyInjection/Compiler/PerInstancePass.php b/DependencyInjection/Compiler/PerInstancePass.php
index 765066ea..c9fbee06 100644
--- a/DependencyInjection/Compiler/PerInstancePass.php
+++ b/DependencyInjection/Compiler/PerInstancePass.php
@@ -13,7 +13,7 @@
  */
 abstract class PerInstancePass implements CompilerPassInterface
 {
-    public function process(ContainerBuilder $container)
+    public function process(ContainerBuilder $container): void
     {
         foreach (self::getSerializers($container) as $scopedContainer) {
             $this->processInstance($scopedContainer);
diff --git a/DependencyInjection/JMSSerializerExtension.php b/DependencyInjection/JMSSerializerExtension.php
index 35ebc51e..1d7fa67c 100644
--- a/DependencyInjection/JMSSerializerExtension.php
+++ b/DependencyInjection/JMSSerializerExtension.php
@@ -33,7 +33,7 @@ final class JMSSerializerExtension extends Extension
     /**
      * {@inheritdoc}
      */
-    public function load(array $rawConfigs, ContainerBuilder $container)
+    public function load(array $rawConfigs, ContainerBuilder $container): void
     {
         $configs = $this->processNestedConfigs($rawConfigs, $container);
 
diff --git a/JMSSerializerBundle.php b/JMSSerializerBundle.php
index a2237a4f..89e97562 100644
--- a/JMSSerializerBundle.php
+++ b/JMSSerializerBundle.php
@@ -16,6 +16,9 @@
 
 class JMSSerializerBundle extends Bundle
 {
+    /**
+     * @return void
+     */
     public function build(ContainerBuilder $builder)
     {
         $builder->addCompilerPass(new AssignVisitorsPass(), PassConfig::TYPE_BEFORE_OPTIMIZATION);