diff --git a/enrol/self/locallib.php b/enrol/self/locallib.php
index 86adfbf819d..a189e7d4066 100644
--- a/enrol/self/locallib.php
+++ b/enrol/self/locallib.php
@@ -67,7 +67,7 @@ class enrol_self_enrol_form extends moodleform {
         if ($instance->password) {
             //change the id of self enrolment key input as there can be multiple self enrolment methods
             $mform->addElement('passwordunmask', 'enrolpassword', get_string('password', 'enrol_self'),
-                    array('id' => $instance->id."_enrolpassword"));
+                    array('id' => 'enrolpassword_'.$instance->id));
         } else {
             $mform->addElement('static', 'nokey', '', get_string('nopassword', 'enrol_self'));
         }
@@ -127,4 +127,4 @@ class enrol_self_enrol_form extends moodleform {
 
         return $errors;
     }
-}
\ No newline at end of file
+}