diff --git a/src/Symfony/Component/DependencyInjection/Loader/Configurator/ContainerConfigurator.php b/src/Symfony/Component/DependencyInjection/Loader/Configurator/ContainerConfigurator.php
index 87b066faf5..07326cae69 100644
--- a/src/Symfony/Component/DependencyInjection/Loader/Configurator/ContainerConfigurator.php
+++ b/src/Symfony/Component/DependencyInjection/Loader/Configurator/ContainerConfigurator.php
@@ -124,7 +124,7 @@ function tagged(string $tag, string $indexAttribute = null, string $defaultIndex
 /**
  * Creates a service locator by tag name.
  */
-function tagged_locator(string $tag, string $indexAttribute, string $defaultIndexMethod = null): ServiceLocatorArgument
+function tagged_locator(string $tag, string $indexAttribute = null, string $defaultIndexMethod = null): ServiceLocatorArgument
 {
     return new ServiceLocatorArgument(new TaggedIteratorArgument($tag, $indexAttribute, $defaultIndexMethod, true));
 }
diff --git a/src/Symfony/Component/DependencyInjection/Loader/YamlFileLoader.php b/src/Symfony/Component/DependencyInjection/Loader/YamlFileLoader.php
index 3fcd9faf18..a6596214bb 100644
--- a/src/Symfony/Component/DependencyInjection/Loader/YamlFileLoader.php
+++ b/src/Symfony/Component/DependencyInjection/Loader/YamlFileLoader.php
@@ -726,25 +726,23 @@ class YamlFileLoader extends FileLoader
             if (\in_array($value->getTag(), ['tagged', 'tagged_locator'], true)) {
                 $forLocator = 'tagged_locator' === $value->getTag();
 
-                if (\is_string($argument) && $argument) {
-                    return new TaggedIteratorArgument($argument, null, null, $forLocator);
-                }
-
                 if (\is_array($argument) && isset($argument['tag']) && $argument['tag']) {
                     if ($diff = array_diff(array_keys($argument), ['tag', 'index_by', 'default_index_method'])) {
                         throw new InvalidArgumentException(sprintf('"!%s" tag contains unsupported key "%s"; supported ones are "tag", "index_by" and "default_index_method".', $value->getTag(), implode('"", "', $diff)));
                     }
 
                     $argument = new TaggedIteratorArgument($argument['tag'], $argument['index_by'] ?? null, $argument['default_index_method'] ?? null, $forLocator);
-
-                    if ($forLocator) {
-                        $argument = new ServiceLocatorArgument($argument);
-                    }
-
-                    return $argument;
+                } elseif (\is_string($argument) && $argument) {
+                    $argument = new TaggedIteratorArgument($argument, null, null, $forLocator);
+                } else {
+                    throw new InvalidArgumentException(sprintf('"!%s" tags only accept a non empty string or an array with a key "tag" in "%s".', $value->getTag(), $file));
                 }
 
-                throw new InvalidArgumentException(sprintf('"!%s" tags only accept a non empty string or an array with a key "tag" in "%s".', $value->getTag(), $file));
+                if ($forLocator) {
+                    $argument = new ServiceLocatorArgument($argument);
+                }
+
+                return $argument;
             }
             if ('service' === $value->getTag()) {
                 if ($isParameter) {
diff --git a/src/Symfony/Component/DependencyInjection/Tests/Dumper/YamlDumperTest.php b/src/Symfony/Component/DependencyInjection/Tests/Dumper/YamlDumperTest.php
index ca41a5b339..56512e89c1 100644
--- a/src/Symfony/Component/DependencyInjection/Tests/Dumper/YamlDumperTest.php
+++ b/src/Symfony/Component/DependencyInjection/Tests/Dumper/YamlDumperTest.php
@@ -104,6 +104,7 @@ class YamlDumperTest extends TestCase
         $container->register('foo_service', 'Foo')->addTag('foo');
         $container->register('foo_service_tagged_iterator', 'Bar')->addArgument($taggedIterator);
         $container->register('foo_service_tagged_locator', 'Bar')->addArgument(new ServiceLocatorArgument($taggedIterator));
+        $container->register('bar_service_tagged_locator', 'Bar')->addArgument(new ServiceLocatorArgument(new TaggedIteratorArgument('foo')));
 
         $dumper = new YamlDumper($container);
         $this->assertStringEqualsFile(self::$fixturesPath.'/yaml/services_with_tagged_argument.yml', $dumper->dump());
diff --git a/src/Symfony/Component/DependencyInjection/Tests/Fixtures/yaml/services_with_tagged_argument.yml b/src/Symfony/Component/DependencyInjection/Tests/Fixtures/yaml/services_with_tagged_argument.yml
index 5e071d3278..0362ebd01b 100644
--- a/src/Symfony/Component/DependencyInjection/Tests/Fixtures/yaml/services_with_tagged_argument.yml
+++ b/src/Symfony/Component/DependencyInjection/Tests/Fixtures/yaml/services_with_tagged_argument.yml
@@ -14,6 +14,9 @@ services:
     foo_service_tagged_locator:
         class: Bar
         arguments: [!tagged_locator { tag: foo, index_by: barfoo, default_index_method: foobar }]
+    bar_service_tagged_locator:
+        class: Bar
+        arguments: [!tagged_locator foo]
     Psr\Container\ContainerInterface:
         alias: service_container
         public: false
diff --git a/src/Symfony/Component/DependencyInjection/Tests/Loader/YamlFileLoaderTest.php b/src/Symfony/Component/DependencyInjection/Tests/Loader/YamlFileLoaderTest.php
index 80e3818908..80b82b96ba 100644
--- a/src/Symfony/Component/DependencyInjection/Tests/Loader/YamlFileLoaderTest.php
+++ b/src/Symfony/Component/DependencyInjection/Tests/Loader/YamlFileLoaderTest.php
@@ -305,6 +305,9 @@ class YamlFileLoaderTest extends TestCase
 
         $taggedIterator = new TaggedIteratorArgument('foo', 'barfoo', 'foobar', true);
         $this->assertEquals(new ServiceLocatorArgument($taggedIterator), $container->getDefinition('foo_service_tagged_locator')->getArgument(0));
+
+        $taggedIterator = new TaggedIteratorArgument('foo', null, null, true);
+        $this->assertEquals(new ServiceLocatorArgument($taggedIterator), $container->getDefinition('bar_service_tagged_locator')->getArgument(0));
     }
 
     public function testNameOnlyTagsAreAllowedAsString()