diff --git a/src/Symfony/Component/DependencyInjection/CHANGELOG.md b/src/Symfony/Component/DependencyInjection/CHANGELOG.md
index 1e45c669e89e..82837aa0e5e9 100644
--- a/src/Symfony/Component/DependencyInjection/CHANGELOG.md
+++ b/src/Symfony/Component/DependencyInjection/CHANGELOG.md
@@ -10,6 +10,7 @@ CHANGELOG
  * Add autoconfigurable attributes
  * Add support for per-env configuration in loaders
  * Add `ContainerBuilder::willBeAvailable()` to help with conditional configuration
+ * Add support an integer return value for default_index_method
 
 5.2.0
 -----
diff --git a/src/Symfony/Component/DependencyInjection/Compiler/PriorityTaggedServiceTrait.php b/src/Symfony/Component/DependencyInjection/Compiler/PriorityTaggedServiceTrait.php
index 806545bee952..30b31eed1628 100644
--- a/src/Symfony/Component/DependencyInjection/Compiler/PriorityTaggedServiceTrait.php
+++ b/src/Symfony/Component/DependencyInjection/Compiler/PriorityTaggedServiceTrait.php
@@ -139,8 +139,12 @@ public static function getDefaultIndex(ContainerBuilder $container, string $serv
 
         $defaultIndex = $rm->invoke(null);
 
+        if (\is_int($defaultIndex)) {
+            $defaultIndex = (string) $defaultIndex;
+        }
+
         if (!\is_string($defaultIndex)) {
-            throw new InvalidArgumentException(implode(sprintf('return a string (got "%s")', get_debug_type($defaultIndex)), $message));
+            throw new InvalidArgumentException(implode(sprintf('return string|int (got "%s")', get_debug_type($defaultIndex)), $message));
         }
 
         return $defaultIndex;
diff --git a/src/Symfony/Component/DependencyInjection/Tests/Compiler/PriorityTaggedServiceTraitTest.php b/src/Symfony/Component/DependencyInjection/Tests/Compiler/PriorityTaggedServiceTraitTest.php
index 2674ea4dde24..5c150a26d0eb 100644
--- a/src/Symfony/Component/DependencyInjection/Tests/Compiler/PriorityTaggedServiceTraitTest.php
+++ b/src/Symfony/Component/DependencyInjection/Tests/Compiler/PriorityTaggedServiceTraitTest.php
@@ -20,6 +20,7 @@
 use Symfony\Component\DependencyInjection\Tests\Fixtures\BarTagClass;
 use Symfony\Component\DependencyInjection\Tests\Fixtures\FooTagClass;
 use Symfony\Component\DependencyInjection\Tests\Fixtures\FooTaggedForInvalidDefaultMethodClass;
+use Symfony\Component\DependencyInjection\Tests\Fixtures\IntTagClass;
 use Symfony\Component\DependencyInjection\TypedReference;
 
 class PriorityTaggedServiceTraitTest extends TestCase
@@ -145,12 +146,15 @@ public function testTheIndexedTagsByDefaultIndexMethod()
         $definition->addTag('my_custom_tag', ['priority' => 100]);
         $definition->addTag('my_custom_tag', []);
 
+        $container->register('service3', IntTagClass::class)->addTag('my_custom_tag');
+
         $priorityTaggedServiceTraitImplementation = new PriorityTaggedServiceTraitImplementation();
 
         $tag = new TaggedIteratorArgument('my_custom_tag', 'foo', 'getFooBar');
         $expected = [
             'bar_tab_class_with_defaultmethod' => new TypedReference('service2', BarTagClass::class),
             'service1' => new TypedReference('service1', FooTagClass::class),
+            '10' => new TypedReference('service3', IntTagClass::class),
         ];
         $services = $priorityTaggedServiceTraitImplementation->test($tag, $container);
         $this->assertSame(array_keys($expected), array_keys($services));
diff --git a/src/Symfony/Component/DependencyInjection/Tests/Fixtures/IntTagClass.php b/src/Symfony/Component/DependencyInjection/Tests/Fixtures/IntTagClass.php
new file mode 100755
index 000000000000..a3114a10b579
--- /dev/null
+++ b/src/Symfony/Component/DependencyInjection/Tests/Fixtures/IntTagClass.php
@@ -0,0 +1,18 @@
+<?php
+
+namespace Symfony\Component\DependencyInjection\Tests\Fixtures;
+
+class IntTagClass
+{
+    public static function getFooBar()
+    {
+        return 10;
+    }
+
+    public static function getPriority(): int
+    {
+        // Should be more than FooTagClass. More because this class is after
+        // FooTagClass (order by name). So we want to ensure it will be before it
+        return 30;
+    }
+}

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