diff --git a/src/Symfony/Component/DependencyInjection/Argument/TaggedIteratorArgument.php b/src/Symfony/Component/DependencyInjection/Argument/TaggedIteratorArgument.php
index a3099686d1..f3b323ce4c 100644
--- a/src/Symfony/Component/DependencyInjection/Argument/TaggedIteratorArgument.php
+++ b/src/Symfony/Component/DependencyInjection/Argument/TaggedIteratorArgument.php
@@ -21,22 +21,22 @@ class TaggedIteratorArgument extends IteratorArgument
     private $tag;
     private $indexAttribute;
     private $defaultIndexMethod;
+    private $useFqcnAsFallback = false;
 
     /**
      * @param string      $tag                The name of the tag identifying the target services
      * @param string|null $indexAttribute     The name of the attribute that defines the key referencing each service in the tagged collection
      * @param string|null $defaultIndexMethod The static method that should be called to get each service's key when their tag doesn't define the previous attribute
+     * @param bool        $useFqcnAsFallback  Whether the FQCN of the service should be used as index when neither the attribute nor the method are defined
      */
-    public function __construct(string $tag, string $indexAttribute = null, string $defaultIndexMethod = null)
+    public function __construct(string $tag, string $indexAttribute = null, string $defaultIndexMethod = null, bool $useFqcnAsFallback = false)
     {
         parent::__construct([]);
 
         $this->tag = $tag;
-
-        if ($indexAttribute) {
-            $this->indexAttribute = $indexAttribute;
-            $this->defaultIndexMethod = $defaultIndexMethod ?: ('getDefault'.str_replace(' ', '', ucwords(preg_replace('/[^a-zA-Z0-9\x7f-\xff]++/', ' ', $indexAttribute))).'Name');
-        }
+        $this->indexAttribute = $indexAttribute;
+        $this->defaultIndexMethod = $defaultIndexMethod ?: ('getDefault'.str_replace(' ', '', ucwords(preg_replace('/[^a-zA-Z0-9\x7f-\xff]++/', ' ', $indexAttribute ?? ''))).'Name');
+        $this->useFqcnAsFallback = $useFqcnAsFallback;
     }
 
     public function getTag()
@@ -53,4 +53,9 @@ class TaggedIteratorArgument extends IteratorArgument
     {
         return $this->defaultIndexMethod;
     }
+
+    public function useFqcnAsFallback(): bool
+    {
+        return $this->useFqcnAsFallback;
+    }
 }
diff --git a/src/Symfony/Component/DependencyInjection/Compiler/PriorityTaggedServiceTrait.php b/src/Symfony/Component/DependencyInjection/Compiler/PriorityTaggedServiceTrait.php
index f9046d3c32..3bf8e3be18 100644
--- a/src/Symfony/Component/DependencyInjection/Compiler/PriorityTaggedServiceTrait.php
+++ b/src/Symfony/Component/DependencyInjection/Compiler/PriorityTaggedServiceTrait.php
@@ -15,6 +15,7 @@ use Symfony\Component\DependencyInjection\Argument\TaggedIteratorArgument;
 use Symfony\Component\DependencyInjection\ContainerBuilder;
 use Symfony\Component\DependencyInjection\Exception\InvalidArgumentException;
 use Symfony\Component\DependencyInjection\Reference;
+use Symfony\Component\DependencyInjection\TypedReference;
 
 /**
  * Trait that allows a generic method to find and sort service by priority option in the tag.
@@ -40,34 +41,48 @@ trait PriorityTaggedServiceTrait
      */
     private function findAndSortTaggedServices($tagName, ContainerBuilder $container)
     {
-        $indexAttribute = $defaultIndexMethod = null;
+        $indexAttribute = $defaultIndexMethod = $useFqcnAsFallback = null;
+
         if ($tagName instanceof TaggedIteratorArgument) {
             $indexAttribute = $tagName->getIndexAttribute();
             $defaultIndexMethod = $tagName->getDefaultIndexMethod();
+            $useFqcnAsFallback = $tagName->useFqcnAsFallback();
             $tagName = $tagName->getTag();
         }
+
         $services = [];
 
         foreach ($container->findTaggedServiceIds($tagName, true) as $serviceId => $attributes) {
             $priority = isset($attributes[0]['priority']) ? $attributes[0]['priority'] : 0;
 
-            if (null === $indexAttribute) {
+            if (null === $indexAttribute && !$useFqcnAsFallback) {
                 $services[$priority][] = new Reference($serviceId);
 
                 continue;
             }
 
-            if (isset($attributes[0][$indexAttribute])) {
-                $services[$priority][$attributes[0][$indexAttribute]] = new Reference($serviceId);
+            $class = $container->getDefinition($serviceId)->getClass();
+            $class = $container->getParameterBag()->resolveValue($class) ?: null;
+
+            if (null !== $indexAttribute && isset($attributes[0][$indexAttribute])) {
+                $services[$priority][$attributes[0][$indexAttribute]] = new TypedReference($serviceId, $class, ContainerBuilder::EXCEPTION_ON_INVALID_REFERENCE, $attributes[0][$indexAttribute]);
 
                 continue;
             }
 
-            if (!$r = $container->getReflectionClass($class = $container->getDefinition($serviceId)->getClass())) {
+            if (!$r = $container->getReflectionClass($class)) {
                 throw new InvalidArgumentException(sprintf('Class "%s" used for service "%s" cannot be found.', $class, $serviceId));
             }
 
+            $class = $r->name;
+
             if (!$r->hasMethod($defaultIndexMethod)) {
+                if ($useFqcnAsFallback) {
+                    $services[$priority][$class] = new TypedReference($serviceId, $class);
+
+                    continue;
+                }
+
                 throw new InvalidArgumentException(sprintf('Method "%s::%s()" not found: tag "%s" on service "%s" is missing "%s" attribute.', $class, $defaultIndexMethod, $tagName, $serviceId, $indexAttribute));
             }
 
@@ -85,7 +100,7 @@ trait PriorityTaggedServiceTrait
                 throw new InvalidArgumentException(sprintf('Method "%s::%s()" should return a string, got %s: tag "%s" on service "%s" is missing "%s" attribute.', $class, $defaultIndexMethod, \gettype($key), $tagName, $serviceId, $indexAttribute));
             }
 
-            $services[$priority][$key] = new Reference($serviceId);
+            $services[$priority][$key] = new TypedReference($serviceId, $class, ContainerBuilder::EXCEPTION_ON_INVALID_REFERENCE, $key);
         }
 
         if ($services) {
diff --git a/src/Symfony/Component/DependencyInjection/Dumper/XmlDumper.php b/src/Symfony/Component/DependencyInjection/Dumper/XmlDumper.php
index 5b9edd0351..57ac2675ae 100644
--- a/src/Symfony/Component/DependencyInjection/Dumper/XmlDumper.php
+++ b/src/Symfony/Component/DependencyInjection/Dumper/XmlDumper.php
@@ -280,36 +280,26 @@ class XmlDumper extends Dumper
             if ($value instanceof ServiceClosureArgument) {
                 $value = $value->getValues()[0];
             }
-            if (\is_array($value)) {
+            if (\is_array($tag = $value)) {
                 $element->setAttribute('type', 'collection');
                 $this->convertParameters($value, $type, $element, 'key');
-            } elseif ($value instanceof TaggedIteratorArgument) {
-                $element->setAttribute('type', 'tagged');
-                $element->setAttribute('tag', $value->getTag());
+            } elseif ($value instanceof TaggedIteratorArgument || ($value instanceof ServiceLocatorArgument && $tag = $value->getTaggedIteratorArgument())) {
+                $element->setAttribute('type', $value instanceof TaggedIteratorArgument ? 'tagged' : 'tagged_locator');
+                $element->setAttribute('tag', $tag->getTag());
 
-                if (null !== $value->getIndexAttribute()) {
-                    $element->setAttribute('index-by', $value->getIndexAttribute());
-                }
+                if (null !== $tag->getIndexAttribute()) {
+                    $element->setAttribute('index-by', $tag->getIndexAttribute());
 
-                if (null !== $value->getDefaultIndexMethod()) {
-                    $element->setAttribute('default-index-method', $value->getDefaultIndexMethod());
+                    if (null !== $tag->getDefaultIndexMethod()) {
+                        $element->setAttribute('default-index-method', $tag->getDefaultIndexMethod());
+                    }
                 }
             } elseif ($value instanceof IteratorArgument) {
                 $element->setAttribute('type', 'iterator');
                 $this->convertParameters($value->getValues(), $type, $element, 'key');
             } elseif ($value instanceof ServiceLocatorArgument) {
-                if ($value->getTaggedIteratorArgument()) {
-                    $element->setAttribute('type', 'tagged_locator');
-                    $element->setAttribute('tag', $value->getTaggedIteratorArgument()->getTag());
-                    $element->setAttribute('index-by', $value->getTaggedIteratorArgument()->getIndexAttribute());
-
-                    if (null !== $value->getTaggedIteratorArgument()->getDefaultIndexMethod()) {
-                        $element->setAttribute('default-index-method', $value->getTaggedIteratorArgument()->getDefaultIndexMethod());
-                    }
-                } else {
-                    $element->setAttribute('type', 'service_locator');
-                    $this->convertParameters($value->getValues(), $type, $element, 'key');
-                }
+                $element->setAttribute('type', 'service_locator');
+                $this->convertParameters($value->getValues(), $type, $element, 'key');
             } elseif ($value instanceof Reference) {
                 $element->setAttribute('type', 'service');
                 $element->setAttribute('id', (string) $value);
diff --git a/src/Symfony/Component/DependencyInjection/Dumper/YamlDumper.php b/src/Symfony/Component/DependencyInjection/Dumper/YamlDumper.php
index b4c899379c..89dae636de 100644
--- a/src/Symfony/Component/DependencyInjection/Dumper/YamlDumper.php
+++ b/src/Symfony/Component/DependencyInjection/Dumper/YamlDumper.php
@@ -232,38 +232,29 @@ class YamlDumper extends Dumper
             $value = $value->getValues()[0];
         }
         if ($value instanceof ArgumentInterface) {
-            if ($value instanceof TaggedIteratorArgument) {
-                if (null !== $value->getIndexAttribute()) {
-                    $taggedValueContent = [
-                        'tag' => $value->getTag(),
-                        'index_by' => $value->getIndexAttribute(),
+            $tag = $value;
+
+            if ($value instanceof TaggedIteratorArgument || ($value instanceof ServiceLocatorArgument && $tag = $value->getTaggedIteratorArgument())) {
+                if (null === $tag->getIndexAttribute()) {
+                    $content = $tag->getTag();
+                } else {
+                    $content = [
+                        'tag' => $tag->getTag(),
+                        'index_by' => $tag->getIndexAttribute(),
                     ];
 
-                    if (null !== $value->getDefaultIndexMethod()) {
-                        $taggedValueContent['default_index_method'] = $value->getDefaultIndexMethod();
+                    if (null !== $tag->getDefaultIndexMethod()) {
+                        $content['default_index_method'] = $tag->getDefaultIndexMethod();
                     }
-
-                    return new TaggedValue('tagged', $taggedValueContent);
                 }
 
-                return new TaggedValue('tagged', $value->getTag());
+                return new TaggedValue($value instanceof TaggedIteratorArgument ? 'tagged' : 'tagged_locator', $content);
             }
+
             if ($value instanceof IteratorArgument) {
                 $tag = 'iterator';
             } elseif ($value instanceof ServiceLocatorArgument) {
                 $tag = 'service_locator';
-                if ($value->getTaggedIteratorArgument()) {
-                    $taggedValueContent = [
-                        'tag' => $value->getTaggedIteratorArgument()->getTag(),
-                        'index_by' => $value->getTaggedIteratorArgument()->getIndexAttribute(),
-                    ];
-
-                    if (null !== $value->getTaggedIteratorArgument()->getDefaultIndexMethod()) {
-                        $taggedValueContent['default_index_method'] = $value->getTaggedIteratorArgument()->getDefaultIndexMethod();
-                    }
-
-                    return new TaggedValue('tagged_locator', $taggedValueContent);
-                }
             } else {
                 throw new RuntimeException(sprintf('Unspecified Yaml tag for type "%s".', \get_class($value)));
             }
diff --git a/src/Symfony/Component/DependencyInjection/Loader/Configurator/ContainerConfigurator.php b/src/Symfony/Component/DependencyInjection/Loader/Configurator/ContainerConfigurator.php
index d4b03fc2c1..87b066faf5 100644
--- a/src/Symfony/Component/DependencyInjection/Loader/Configurator/ContainerConfigurator.php
+++ b/src/Symfony/Component/DependencyInjection/Loader/Configurator/ContainerConfigurator.php
@@ -126,7 +126,7 @@ function tagged(string $tag, string $indexAttribute = null, string $defaultIndex
  */
 function tagged_locator(string $tag, string $indexAttribute, string $defaultIndexMethod = null): ServiceLocatorArgument
 {
-    return new ServiceLocatorArgument(new TaggedIteratorArgument($tag, $indexAttribute, $defaultIndexMethod));
+    return new ServiceLocatorArgument(new TaggedIteratorArgument($tag, $indexAttribute, $defaultIndexMethod, true));
 }
 
 /**
diff --git a/src/Symfony/Component/DependencyInjection/Loader/XmlFileLoader.php b/src/Symfony/Component/DependencyInjection/Loader/XmlFileLoader.php
index ced8b0142d..92c27e6ebf 100644
--- a/src/Symfony/Component/DependencyInjection/Loader/XmlFileLoader.php
+++ b/src/Symfony/Component/DependencyInjection/Loader/XmlFileLoader.php
@@ -533,19 +533,20 @@ class XmlFileLoader extends FileLoader
                         throw new InvalidArgumentException(sprintf('Tag "<%s>" with type="service_locator" only accepts maps of type="service" references in "%s".', $name, $file));
                     }
                     break;
-                case 'tagged_locator':
-                    if (!$arg->getAttribute('tag') || !$arg->getAttribute('index-by')) {
-                        throw new InvalidArgumentException(sprintf('Tag "<%s>" with type="tagged_locator" has no or empty "tag" or "index-by" attributes in "%s".', $name, $file));
-                    }
-
-                    $arguments[$key] = new ServiceLocatorArgument(new TaggedIteratorArgument($arg->getAttribute('tag'), $arg->getAttribute('index-by'), $arg->getAttribute('default-index-method') ?: null));
-                    break;
                 case 'tagged':
+                case 'tagged_locator':
+                    $type = $arg->getAttribute('type');
+                    $forLocator = 'tagged_locator' === $type;
+
                     if (!$arg->getAttribute('tag')) {
-                        throw new InvalidArgumentException(sprintf('Tag "<%s>" with type="tagged" has no or empty "tag" attribute in "%s".', $name, $file));
+                        throw new InvalidArgumentException(sprintf('Tag "<%s>" with type="%s" has no or empty "tag" attribute in "%s".', $name, $type, $file));
                     }
 
-                    $arguments[$key] = new TaggedIteratorArgument($arg->getAttribute('tag'), $arg->getAttribute('index-by') ?: null, $arg->getAttribute('default-index-method') ?: null);
+                    $arguments[$key] = new TaggedIteratorArgument($arg->getAttribute('tag'), $arg->getAttribute('index-by') ?: null, $arg->getAttribute('default-index-method') ?: null, $forLocator);
+
+                    if ($forLocator) {
+                        $arguments[$key] = new ServiceLocatorArgument($arguments[$key]);
+                    }
                     break;
                 case 'binary':
                     if (false === $value = base64_decode($arg->nodeValue)) {
diff --git a/src/Symfony/Component/DependencyInjection/Loader/YamlFileLoader.php b/src/Symfony/Component/DependencyInjection/Loader/YamlFileLoader.php
index 4d9da4e314..ecd66dd276 100644
--- a/src/Symfony/Component/DependencyInjection/Loader/YamlFileLoader.php
+++ b/src/Symfony/Component/DependencyInjection/Loader/YamlFileLoader.php
@@ -711,31 +711,28 @@ class YamlFileLoader extends FileLoader
                     throw new InvalidArgumentException(sprintf('"!service_locator" tag only accepts maps of "@service" references in "%s".', $file));
                 }
             }
-            if ('tagged' === $value->getTag()) {
+            if (\in_array($value->getTag(), ['tagged', 'tagged_locator'], true)) {
+                $forLocator = 'tagged_locator' === $value->getTag();
+
                 if (\is_string($argument) && $argument) {
-                    return new TaggedIteratorArgument($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('"!tagged" tag contains unsupported key "%s"; supported ones are "tag", "index_by" and "default_index_method".', implode('"", "', $diff)));
+                        throw new InvalidArgumentException(sprintf('"!%s" tag contains unsupported key "%s"; supported ones are "tag", "index_by" and "default_index_method".', $value->getTag(), implode('"", "', $diff)));
                     }
 
-                    return new TaggedIteratorArgument($argument['tag'], $argument['index_by'] ?? null, $argument['default_index_method'] ?? null);
-                }
+                    $argument = new TaggedIteratorArgument($argument['tag'], $argument['index_by'], $argument['default_index_method'] ?? null, $forLocator);
 
-                throw new InvalidArgumentException(sprintf('"!tagged" tags only accept a non empty string or an array with a key "tag" in "%s".', $file));
-            }
-            if ('tagged_locator' === $value->getTag()) {
-                if (\is_array($argument) && isset($argument['tag'], $argument['index_by']) && $argument['tag'] && $argument['index_by']) {
-                    if ($diff = array_diff(array_keys($argument), ['tag', 'index_by', 'default_index_method'])) {
-                        throw new InvalidArgumentException(sprintf('"!tagged_locator" tag contains unsupported key "%s"; supported ones are "tag", "index_by" and "default_index_method".', implode('"", "', $diff)));
+                    if ($forLocator) {
+                        $argument = new ServiceLocatorArgument($argument);
                     }
 
-                    return new ServiceLocatorArgument(new TaggedIteratorArgument($argument['tag'], $argument['index_by'], $argument['default_index_method'] ?? null));
+                    return $argument;
                 }
 
-                throw new InvalidArgumentException(sprintf('"!tagged_locator" tags only accept an array with at least keys "tag" and "index_by" in "%s".', $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 ('service' === $value->getTag()) {
                 if ($isParameter) {
diff --git a/src/Symfony/Component/DependencyInjection/Tests/Compiler/IntegrationTest.php b/src/Symfony/Component/DependencyInjection/Tests/Compiler/IntegrationTest.php
index a2bbbe20cf..feeb163edb 100644
--- a/src/Symfony/Component/DependencyInjection/Tests/Compiler/IntegrationTest.php
+++ b/src/Symfony/Component/DependencyInjection/Tests/Compiler/IntegrationTest.php
@@ -350,6 +350,32 @@ class IntegrationTest extends TestCase
         ];
         $this->assertSame(['bar_tab_class_with_defaultmethod' => $container->get(BarTagClass::class), 'foo' => $container->get(FooTagClass::class)], $same);
     }
+
+    public function testTaggedServiceLocatorWithFqcnFallback()
+    {
+        $container = new ContainerBuilder();
+        $container->register(BarTagClass::class)
+            ->setPublic(true)
+            ->addTag('foo_bar')
+        ;
+        $container->register(FooBarTaggedClass::class)
+            ->addArgument(new ServiceLocatorArgument(new TaggedIteratorArgument('foo_bar', null, null, true)))
+            ->setPublic(true)
+        ;
+
+        $container->compile();
+
+        $s = $container->get(FooBarTaggedClass::class);
+
+        /** @var ServiceLocator $serviceLocator */
+        $serviceLocator = $s->getParam();
+        $this->assertTrue($s->getParam() instanceof ServiceLocator, sprintf('Wrong instance, should be an instance of ServiceLocator, %s given', \is_object($serviceLocator) ? \get_class($serviceLocator) : \gettype($serviceLocator)));
+
+        $same = [
+            BarTagClass::class => $serviceLocator->get(BarTagClass::class),
+        ];
+        $this->assertSame([BarTagClass::class => $container->get(BarTagClass::class)], $same);
+    }
 }
 
 class ServiceSubscriberStub implements ServiceSubscriberInterface
diff --git a/src/Symfony/Component/DependencyInjection/Tests/Compiler/PriorityTaggedServiceTraitTest.php b/src/Symfony/Component/DependencyInjection/Tests/Compiler/PriorityTaggedServiceTraitTest.php
index adf9696acd..57ca9af427 100644
--- a/src/Symfony/Component/DependencyInjection/Tests/Compiler/PriorityTaggedServiceTraitTest.php
+++ b/src/Symfony/Component/DependencyInjection/Tests/Compiler/PriorityTaggedServiceTraitTest.php
@@ -93,6 +93,6 @@ class PriorityTaggedServiceTraitImplementation
 
     public function test($tagName, ContainerBuilder $container)
     {
-        return self::findAndSortTaggedServices($tagName, $container);
+        return $this->findAndSortTaggedServices($tagName, $container);
     }
 }
diff --git a/src/Symfony/Component/DependencyInjection/Tests/Loader/XmlFileLoaderTest.php b/src/Symfony/Component/DependencyInjection/Tests/Loader/XmlFileLoaderTest.php
index 3e326ed85a..681a43b332 100644
--- a/src/Symfony/Component/DependencyInjection/Tests/Loader/XmlFileLoaderTest.php
+++ b/src/Symfony/Component/DependencyInjection/Tests/Loader/XmlFileLoaderTest.php
@@ -329,6 +329,8 @@ class XmlFileLoaderTest extends TestCase
 
         $taggedIterator = new TaggedIteratorArgument('foo_tag', 'barfoo', 'foobar');
         $this->assertEquals($taggedIterator, $container->getDefinition('foo_tagged_iterator')->getArgument(0));
+
+        $taggedIterator = new TaggedIteratorArgument('foo_tag', 'barfoo', 'foobar', true);
         $this->assertEquals(new ServiceLocatorArgument($taggedIterator), $container->getDefinition('foo_tagged_locator')->getArgument(0));
     }
 
diff --git a/src/Symfony/Component/DependencyInjection/Tests/Loader/YamlFileLoaderTest.php b/src/Symfony/Component/DependencyInjection/Tests/Loader/YamlFileLoaderTest.php
index 0da99f437b..83e034c482 100644
--- a/src/Symfony/Component/DependencyInjection/Tests/Loader/YamlFileLoaderTest.php
+++ b/src/Symfony/Component/DependencyInjection/Tests/Loader/YamlFileLoaderTest.php
@@ -293,6 +293,8 @@ class YamlFileLoaderTest extends TestCase
 
         $taggedIterator = new TaggedIteratorArgument('foo', 'barfoo', 'foobar');
         $this->assertEquals($taggedIterator, $container->getDefinition('foo_service_tagged_iterator')->getArgument(0));
+
+        $taggedIterator = new TaggedIteratorArgument('foo', 'barfoo', 'foobar', true);
         $this->assertEquals(new ServiceLocatorArgument($taggedIterator), $container->getDefinition('foo_service_tagged_locator')->getArgument(0));
     }