diff --git a/phpBB/phpbb/di/container_builder.php b/phpBB/phpbb/di/container_builder.php
index c665c8444c..62bba5baf9 100644
--- a/phpBB/phpbb/di/container_builder.php
+++ b/phpBB/phpbb/di/container_builder.php
@@ -162,7 +162,7 @@ class container_builder
 				$installed_exts = $this->get_installed_extensions();
 				foreach ($installed_exts as $ext_name => $path)
 				{
-					$extension_class = '\\' . str_replace('/', '\\', $ext_name) . '\\di\extension';
+					$extension_class = '\\' . str_replace('/', '\\', $ext_name) . '\\di\\extension';
 
 					if (!class_exists($extension_class))
 					{
diff --git a/tests/di/create_container_test.php b/tests/di/create_container_test.php
index 4e47751999..9cc714db40 100644
--- a/tests/di/create_container_test.php
+++ b/tests/di/create_container_test.php
@@ -16,6 +16,7 @@ namespace
 	define('PHPBB_ENVIRONMENT', 'production');
 
 	require_once dirname(__FILE__) . '/../../phpBB/includes/functions.php';
+	require_once dirname(__FILE__) . '/fixtures/ext/vendor/enabled_4/di/extension.php';
 
 	class phpbb_di_container_test extends \phpbb_test_case
 	{
@@ -61,6 +62,7 @@ namespace
 			$this->assertTrue($container->hasParameter('enabled'));
 			$this->assertTrue($container->hasParameter('enabled_2'));
 			$this->assertTrue($container->hasParameter('enabled_3'));
+			$this->assertTrue($container->hasParameter('enabled_4'));
 			$this->assertFalse($container->hasParameter('disabled'));
 			$this->assertFalse($container->hasParameter('available'));
 
@@ -204,6 +206,7 @@ namespace phpbb\db\driver
 				array('ext_name' => 'vendor/enabled'),
 				array('ext_name' => 'vendor/enabled-2'),
 				array('ext_name' => 'vendor/enabled-3'),
+				array('ext_name' => 'vendor/enabled_4'),
 			);
 		}
 	}
diff --git a/tests/di/fixtures/ext/vendor/enabled_4/di/extension.php b/tests/di/fixtures/ext/vendor/enabled_4/di/extension.php
new file mode 100644
index 0000000000..8342625687
--- /dev/null
+++ b/tests/di/fixtures/ext/vendor/enabled_4/di/extension.php
@@ -0,0 +1,31 @@
+<?php
+/**
+*
+* This file is part of the phpBB Forum Software package.
+*
+* @copyright (c) phpBB Limited <https://www.phpbb.com>
+* @license GNU General Public License, version 2 (GPL-2.0)
+*
+* For full copyright and license information, please see
+* the docs/CREDITS.txt file.
+*
+*/
+
+namespace vendor\enabled_4\di;
+
+use phpbb\extension\di\extension_base;
+use Symfony\Component\Config\FileLocator;
+use Symfony\Component\DependencyInjection\ContainerBuilder;
+use Symfony\Component\DependencyInjection\Loader\YamlFileLoader;
+
+/**
+* Container core extension
+*/
+class extension extends extension_base
+{
+	protected function load_services(ContainerBuilder $container)
+	{
+		$loader = new YamlFileLoader($container, new FileLocator(phpbb_realpath($this->ext_path)));
+		$loader->load('environment.yml');
+	}
+}
diff --git a/tests/di/fixtures/ext/vendor/enabled_4/environment.yml b/tests/di/fixtures/ext/vendor/enabled_4/environment.yml
new file mode 100644
index 0000000000..d0affe4fd6
--- /dev/null
+++ b/tests/di/fixtures/ext/vendor/enabled_4/environment.yml
@@ -0,0 +1,2 @@
+parameters:
+    enabled_4: true