diff --git a/phpBB/includes/extension/finder.php b/phpBB/includes/extension/finder.php
index d9aacc38ff..02a9ebb8c3 100644
--- a/phpBB/includes/extension/finder.php
+++ b/phpBB/includes/extension/finder.php
@@ -23,6 +23,7 @@ if (!defined('IN_PHPBB'))
 class phpbb_extension_finder
 {
 	protected $extension_manager;
+	protected $filesystem;
 	protected $phpbb_root_path;
 	protected $cache;
 	protected $php_ext;
@@ -54,15 +55,17 @@ class phpbb_extension_finder
 	* @param phpbb_extension_manager $extension_manager An extension manager
 	*            instance that provides the finder with a list of active
 	*            extensions and their locations
+	* @param phpbb_filesystem $filesystem Filesystem instance
 	* @param string $phpbb_root_path Path to the phpbb root directory
 	* @param phpbb_cache_driver_interface $cache A cache instance or null
 	* @param string $php_ext php file extension
 	* @param string $cache_name The name of the cache variable, defaults to
 	*                           _ext_finder
 	*/
-	public function __construct(phpbb_extension_manager $extension_manager, $phpbb_root_path = '', phpbb_cache_driver_interface $cache = null, $php_ext = '.php', $cache_name = '_ext_finder')
+	public function __construct(phpbb_extension_manager $extension_manager, phpbb_filesystem $filesystem, $phpbb_root_path = '', phpbb_cache_driver_interface $cache = null, $php_ext = '.php', $cache_name = '_ext_finder')
 	{
 		$this->extension_manager = $extension_manager;
+		$this->filesystem = $filesystem;
 		$this->phpbb_root_path = $phpbb_root_path;
 		$this->cache = $cache;
 		$this->php_ext = $php_ext;
@@ -227,7 +230,7 @@ class phpbb_extension_finder
 	*/
 	protected function sanitise_directory($directory)
 	{
-		$directory = phpbb_clean_path($directory);
+		$directory = $this->filesystem->clean_path($directory);
 		$dir_len = strlen($directory);
 
 		if ($dir_len > 1 && $directory[$dir_len - 1] === '/')