diff --git a/report/grading/report.php b/report/grading/report.php
index a760beb..54ada97 100644
--- a/report/grading/report.php
+++ b/report/grading/report.php
@@ -335,7 +335,8 @@ protected function get_usage_ids_where_question_in_state($summarystate, $slot,
                     ) as tcreated";
             $orderby = "tcreated";
         } else if ($orderby === 'usercode') {
-            $qubaids->from .= " JOIN {local_quizanon_usercodes} lqau ON lqau.userid = quiza.userid";
+            $qubaids->from
+                .= " JOIN {local_quizanon_usercodes} lqau ON lqau.userid = quiza.userid AND quiza.quiz = lqau.quizid";
             $orderby = 'lqau.code';
         }
         return $dm->load_questions_usages_where_question_in_state($qubaids, $summarystate,