diff --git a/src/Symfony/ContainerMeta.php b/src/Symfony/ContainerMeta.php
index e7d86bb..433c021 100644
--- a/src/Symfony/ContainerMeta.php
+++ b/src/Symfony/ContainerMeta.php
@@ -125,7 +125,10 @@ private function init(array $containerXmlPaths): void
         }
     }
 
-    private function addServiceLocator(string $key, string $id, Reference $reference): void
+    /**
+     * @param array-key $id
+     */
+    private function addServiceLocator(string $key, mixed $id, Reference $reference): void
     {
         $this->serviceLocators[$key][$id] = (string) $reference;
 
diff --git a/tests/acceptance/container.xml b/tests/acceptance/container.xml
index 409c7d9..7b34076 100644
--- a/tests/acceptance/container.xml
+++ b/tests/acceptance/container.xml
@@ -84,6 +84,7 @@
         <argument key="dummy_service_with_locator2" type="service" id="Psalm\SymfonyPsalmPlugin\Tests\Fixture\DummyPrivateService"/>
         <argument key="dummy_service_with_locator3" type="service_closure" id="Psalm\SymfonyPsalmPlugin\Tests\Fixture\DummyPrivateService"/>
         <argument key="validator" type="service" id="debug.validator"/>
+        <argument key="1234" type="service" id="Psalm\SymfonyPsalmPlugin\Tests\Fixture\DummyPrivateService"/>
       </argument>
     </service>
   </services>