diff --git a/lib/tablelib.php b/lib/tablelib.php
index 8e28ab497e1..476fd9bcfa6 100644
--- a/lib/tablelib.php
+++ b/lib/tablelib.php
@@ -1307,7 +1307,7 @@ class flexible_table {
             if (array_key_exists($sortby, $sortdata)) {
                 // This key already exists somewhere. Change its sortorder and bring it to the top.
                 //$sortorder = $sortdata[$sortby] = $sortorder;
-                unset($sortdata['sortby'][$sortby]);
+                unset($sortdata[$sortby]);
             }
             $sortdata = array_merge([$sortby => $sortorder], $sortdata);
         }