diff --git a/course/lib.php b/course/lib.php
index 3e79a825222..07a2af96041 100644
--- a/course/lib.php
+++ b/course/lib.php
@@ -2725,7 +2725,7 @@ function move_courses ($courseids, $categoryid) {
                     // figure out a sortorder that we can use in the destination category
                     $sortorder = get_field_sql('SELECT MIN(sortorder)-1 AS min
                                                     FROM ' . $CFG->prefix . 'course WHERE category=' . $categoryid);
-                    if ($sortorder === false) {
+                    if (is_null($sortorder) || $sortorder === false) {
                         // the category is empty
                         // rather than let the db default to 0
                         // set it to > 100 and avoid extra work in fix_coursesortorder()