diff --git a/lib/completion/completion_criteria_duration.php b/lib/completion/completion_criteria_duration.php
index 6ce85e9b2cd..bc2c8a07883 100644
--- a/lib/completion/completion_criteria_duration.php
+++ b/lib/completion/completion_criteria_duration.php
@@ -90,7 +90,12 @@ class completion_criteria_duration extends completion_criteria {
     private function get_timeenrolled($completion) {
         global $DB;
 
-        return $DB->get_field('user_enrolments', 'timestart', array('courseid' => $this->course, 'userid' => $completion->userid));
+        return $DB->get_field_sql('
+            SELECT eu.timestart
+              FROM {user_enrolments} eu
+              JOIN {enrol} e ON eu.enrolid = e.id
+             WHERE e.courseid = ?
+               AND eu.userid = ?', array($this->course, $completion->userid));
     }
 
     /**