diff --git a/rector.php b/rector.php
index 83826068..6d92b1a9 100644
--- a/rector.php
+++ b/rector.php
@@ -13,21 +13,21 @@
 use Rector\Symfony\Set\SymfonySetList;
 
 return static function (RectorConfig $config): void {
-    $config->sets([
-        SetList::DEAD_CODE,
-        LevelSetList::UP_TO_PHP_81,
-        SymfonyLevelSetList::UP_TO_SYMFONY_54,
-        SymfonySetList::SYMFONY_CODE_QUALITY,
-        SymfonySetList::SYMFONY_CONSTRUCTOR_INJECTION,
-        DoctrineSetList::DOCTRINE_CODE_QUALITY,
-        DoctrineSetList::ANNOTATIONS_TO_ATTRIBUTES,
-        PHPUnitSetList::PHPUNIT_SPECIFIC_METHOD,
-        PHPUnitLevelSetList::UP_TO_PHPUNIT_90,
-        PHPUnitSetList::PHPUNIT_CODE_QUALITY,
-        PHPUnitSetList::PHPUNIT_EXCEPTION,
-        PHPUnitSetList::REMOVE_MOCKS,
-        PHPUnitSetList::PHPUNIT_YIELD_DATA_PROVIDER,
-    ]);
+    $config->import(SetList::DEAD_CODE);
+    $config->import(LevelSetList::UP_TO_PHP_81);
+    $config->import(SymfonyLevelSetList::UP_TO_SYMFONY_54);
+    $config->import(SymfonySetList::SYMFONY_CODE_QUALITY);
+    $config->import(SymfonySetList::SYMFONY_CONSTRUCTOR_INJECTION);
+    $config->import(SymfonySetList::SYMFONY_STRICT);
+    $config->import(SymfonySetList::ANNOTATIONS_TO_ATTRIBUTES);
+    $config->import(DoctrineSetList::DOCTRINE_CODE_QUALITY);
+    $config->import(DoctrineSetList::ANNOTATIONS_TO_ATTRIBUTES);
+    $config->import(PHPUnitSetList::PHPUNIT_SPECIFIC_METHOD);
+    $config->import(PHPUnitLevelSetList::UP_TO_PHPUNIT_90);
+    $config->import(PHPUnitSetList::PHPUNIT_CODE_QUALITY);
+    $config->import(PHPUnitSetList::PHPUNIT_EXCEPTION);
+    $config->import(PHPUnitSetList::REMOVE_MOCKS);
+    $config->import(PHPUnitSetList::PHPUNIT_YIELD_DATA_PROVIDER);
     $config->parallel();
     $config->paths([__DIR__ . '/src', __DIR__ . '/performance', __DIR__ . '/tests']);
     $config->skip([
diff --git a/src/Bundle/JoseFramework/DependencyInjection/Source/KeyManagement/JWKSource/JWKSet.php b/src/Bundle/JoseFramework/DependencyInjection/Source/KeyManagement/JWKSource/JWKSet.php
index c5abbc16..97142000 100644
--- a/src/Bundle/JoseFramework/DependencyInjection/Source/KeyManagement/JWKSource/JWKSet.php
+++ b/src/Bundle/JoseFramework/DependencyInjection/Source/KeyManagement/JWKSource/JWKSet.php
@@ -4,6 +4,8 @@
 
 namespace Jose\Bundle\JoseFramework\DependencyInjection\Source\KeyManagement\JWKSource;
 
+use function is_int;
+use function is_string;
 use Jose\Bundle\JoseFramework\DependencyInjection\Source\AbstractSource;
 use Jose\Component\Core\JWK;
 use Jose\Component\KeyManagement\JWKFactory;
@@ -41,7 +43,11 @@ public function addConfiguration(NodeDefinition $node): void
             ->info('The key set service.')
             ->isRequired()
             ->end()
-            ->integerNode('index')
+            ->variableNode('index')
+            ->validate()
+            ->ifTrue(fn (mixed $v): bool => ! is_int($v) && ! is_string($v))
+            ->thenInvalid('Invalid keyset index.')
+            ->end()
             ->info('The index of the key in the key set.')
             ->isRequired()
             ->end()