diff --git a/mod/forum/lib.php b/mod/forum/lib.php
index 4923a1bde93..1c38cd14de3 100644
--- a/mod/forum/lib.php
+++ b/mod/forum/lib.php
@@ -4364,6 +4364,7 @@ function forum_update_post($newpost, $mform, $unused = null) {
         'timestart',
         'timeend',
         'pinned',
+        'attachments',
     ];
     foreach ($modifiablefields as $field) {
         if (isset($newpost->{$field})) {