diff --git a/lib/moodlelib.php b/lib/moodlelib.php
index 6b3c6eecabe..763d7263a30 100644
--- a/lib/moodlelib.php
+++ b/lib/moodlelib.php
@@ -5716,7 +5716,7 @@ function get_mailer($action='get') {
  * @param string $subject plain text subject line of the email
  * @param string $messagetext plain text version of the message
  * @param string $messagehtml complete html version of the message (optional)
- * @param string $attachment a file on the filesystem, relative to $CFG->dataroot
+ * @param string $attachment a file on the filesystem, either relative to $CFG->dataroot or a full path to a file in $CFG->tempdir
  * @param string $attachname the name of the file (extension indicates MIME)
  * @param bool $usetrueaddress determines whether $from email address should
  *          be sent out. Will be overruled by user profile setting for maildisplay