diff --git a/library/HTMLPurifier.composer.php b/library/HTMLPurifier.composer.php
index 6706f4e3..52acc56b 100644
--- a/library/HTMLPurifier.composer.php
+++ b/library/HTMLPurifier.composer.php
@@ -1,4 +1,4 @@
 <?php
 if (!defined('HTMLPURIFIER_PREFIX')) {
-    define('HTMLPURIFIER_PREFIX', __DIR__);
+    define('HTMLPURIFIER_PREFIX', dirname(__FILE__));
 }