diff --git a/mod/quiz/report/grading/report.php b/mod/quiz/report/grading/report.php
index 9c9abbb752b..10225905d51 100644
--- a/mod/quiz/report/grading/report.php
+++ b/mod/quiz/report/grading/report.php
@@ -665,7 +665,7 @@ class quiz_grading_report extends quiz_default_report {
         $a = new stdClass();
         $a->attempt = $attempt->attempt;
         $a->fullname = fullname($attempt);
-        $a->idnumber = $attempt->idnumber;
+        $a->idnumber = s($attempt->idnumber);
 
         $showidnumbers = $showidnumbers && !empty($attempt->idnumber);