diff --git a/src/Symfony/Component/DependencyInjection/Attribute/TaggedItem.php b/src/Symfony/Component/DependencyInjection/Attribute/TaggedItem.php
index b7ba825ae8e5f..a848e68d63516 100644
--- a/src/Symfony/Component/DependencyInjection/Attribute/TaggedItem.php
+++ b/src/Symfony/Component/DependencyInjection/Attribute/TaggedItem.php
@@ -20,7 +20,7 @@
 class TaggedItem
 {
     public function __construct(
-        public string $index,
+        public ?string $index = null,
         public ?int $priority = null,
     ) {
     }
diff --git a/src/Symfony/Component/DependencyInjection/Tests/Compiler/PriorityTaggedServiceTraitTest.php b/src/Symfony/Component/DependencyInjection/Tests/Compiler/PriorityTaggedServiceTraitTest.php
index 1ef1521b7d86c..bd3b82d64f74a 100644
--- a/src/Symfony/Component/DependencyInjection/Tests/Compiler/PriorityTaggedServiceTraitTest.php
+++ b/src/Symfony/Component/DependencyInjection/Tests/Compiler/PriorityTaggedServiceTraitTest.php
@@ -205,6 +205,9 @@ public function testTaggedItemAttributes()
                 HelloNamedService::class => (new ChildDefinition(''))->addTag('my_custom_tag'),
                 \stdClass::class => (new ChildDefinition(''))->addTag('my_custom_tag2'),
             ]);
+        $container->register('service3', HelloNamedService2::class)
+            ->setAutoconfigured(true)
+            ->addTag('my_custom_tag');
 
         (new ResolveInstanceofConditionalsPass())->process($container);
 
@@ -212,6 +215,7 @@ public function testTaggedItemAttributes()
 
         $tag = new TaggedIteratorArgument('my_custom_tag', 'foo', 'getFooBar');
         $expected = [
+            'service3' => new TypedReference('service3', HelloNamedService2::class),
             'hello' => new TypedReference('service2', HelloNamedService::class),
             'service1' => new TypedReference('service1', FooTagClass::class),
         ];
@@ -235,3 +239,8 @@ public function test($tagName, ContainerBuilder $container)
 class HelloNamedService extends \stdClass
 {
 }
+
+#[TaggedItem(priority: 2)]
+class HelloNamedService2
+{
+}