diff --git a/mod/lesson/db/upgrade.php b/mod/lesson/db/upgrade.php
index 1321dadf815..930af273da4 100644
--- a/mod/lesson/db/upgrade.php
+++ b/mod/lesson/db/upgrade.php
@@ -390,7 +390,7 @@ function xmldb_lesson_upgrade($oldversion) {
     if ($oldversion < 2016052301) {
 
         // Delete orphaned lesson answer and response files.
-        $sql = "SELECT DISTINCT f.*
+        $sql = "SELECT DISTINCT f.contextid, f.component, f.filearea, f.itemid
                   FROM {files} f
              LEFT JOIN {lesson_answers} la ON f.itemid = la.id
                  WHERE component = :component