diff --git a/lib/classes/event/manager.php b/lib/classes/event/manager.php
index 400723d181b..c2be7ab5666 100644
--- a/lib/classes/event/manager.php
+++ b/lib/classes/event/manager.php
@@ -282,6 +282,7 @@ class manager {
                 if ($CFG->admin !== 'admin' and strpos($observer['includefile'], '/admin/') === 0) {
                     $observer['includefile'] = preg_replace('|^/admin/|', '/'.$CFG->admin.'/', $observer['includefile']);
                 }
+                $observer['includefile'] = $CFG->dirroot . '/' . ltrim($observer['includefile'], '/');
                 if (!file_exists($observer['includefile'])) {
                     debugging("Invalid 'includefile' detected in $file observer definition", DEBUG_DEVELOPER);
                     continue;