diff --git a/mod/assign/locallib.php b/mod/assign/locallib.php
index 1db283bbb82..5f340477f0a 100644
--- a/mod/assign/locallib.php
+++ b/mod/assign/locallib.php
@@ -1516,14 +1516,18 @@ class assign {
         $timenow   = time();
 
         // Collect all submissions from the past 24 hours that require mailing.
+        // Submissions are excluded if the assignment is hidden in the gradebook.
         $sql = 'SELECT g.id as gradeid, a.course, a.name, a.blindmarking, a.revealidentities,
                        g.*, g.timemodified as lastmodified
                  FROM {assign} a
                  JOIN {assign_grades} g ON g.assignment = a.id
-                 LEFT JOIN {assign_user_flags} uf ON uf.assignment = a.id AND uf.userid = g.userid
-                WHERE g.timemodified >= :yesterday AND
-                      g.timemodified <= :today AND
-                      uf.mailed = 0';
+            LEFT JOIN {assign_user_flags} uf ON uf.assignment = a.id AND uf.userid = g.userid
+                 JOIN {course_modules} cm ON cm.course = a.course
+                 JOIN {modules} md ON md.id = cm.module
+                 JOIN {grade_items} gri ON gri.iteminstance = a.id AND gri.courseid = a.course AND gri.itemmodule = md.name
+                 WHERE g.timemodified >= :yesterday AND
+                       g.timemodified <= :today AND
+                       uf.mailed = 0 AND gri.hidden = 0';
 
         $params = array('yesterday' => $yesterday, 'today' => $timenow);
         $submissions = $DB->get_records_sql($sql, $params);