diff --git a/src/VatBundle.php b/src/VatBundle.php
index 3353ee4..d88a8b4 100644
--- a/src/VatBundle.php
+++ b/src/VatBundle.php
@@ -1,12 +1,13 @@
 <?php
 namespace Ibericode\Vat\Bundle;
 
-use Ibericode\Vat\Bundle\DependencyInjection\VatExtension; 
+use Ibericode\Vat\Bundle\DependencyInjection\VatExtension;
+use Symfony\Component\DependencyInjection\Extension\ExtensionInterface;
 
 class VatBundle extends \Symfony\Component\HttpKernel\Bundle\Bundle
 {
-    public function getContainerExtension()
+    public function getContainerExtension() : ?ExtensionInterface
     {
         return new VatExtension();
     }
-}
\ No newline at end of file
+}