diff --git a/course/lib.php b/course/lib.php
index ea300310cb4..1cbd5c85b82 100644
--- a/course/lib.php
+++ b/course/lib.php
@@ -895,7 +895,7 @@ function make_categories_list(&$list, &$parents, $category=NULL, $path="") {
     if ($categories = get_categories("$category->id")) {   // Print all the children recursively
         foreach ($categories as $cat) {
             if (!empty($category->id)) {
-                if (!empty($parents[$category->id])) {
+                if (isset($parents[$category->id])) {
                     $parents[$cat->id]   = $parents[$category->id];
                 }
                 $parents[$cat->id][] = $category->id;