diff --git a/auth/db/auth.php b/auth/db/auth.php
index a88a9f50b66..b23b65ce32e 100644
--- a/auth/db/auth.php
+++ b/auth/db/auth.php
@@ -17,6 +17,7 @@ if (!defined('MOODLE_INTERNAL')) {
 }
 
 require_once($CFG->libdir.'/authlib.php');
+require_once($CFG->libdir.'/adodb/adodb.inc.php');
 
 /**
  * External database authentication plugin.