diff --git a/src/Markdown/DependencyInjection/MarkdownExtension.php b/src/Markdown/DependencyInjection/MarkdownExtension.php
index 7e06019..1ef2942 100644
--- a/src/Markdown/DependencyInjection/MarkdownExtension.php
+++ b/src/Markdown/DependencyInjection/MarkdownExtension.php
@@ -22,7 +22,7 @@
 
 use function dirname;
 
-class MarkdownExtension extends Extension implements PrependExtensionInterface, CompilerPassInterface
+final class MarkdownExtension extends Extension implements PrependExtensionInterface, CompilerPassInterface
 {
     /** @param mixed[] $configs */
     public function load(array $configs, ContainerBuilder $container): void