diff --git a/lib/classes/UserFilter.php b/lib/classes/UserFilter.php
index 7745587a2b3852ba4fc89f6e79ee5c5eaa6300a0..ba3f0636ff21c2bc9aa6b30bff2b7a42f767f28d 100644
--- a/lib/classes/UserFilter.php
+++ b/lib/classes/UserFilter.php
@@ -107,7 +107,7 @@ class UserFilter
     public function getFields()
     {
         uasort($this->fields, function ($a, $b) {
-            return $a->sortOrder - $b->sortOrder;
+            return $a::$sortOrder - $b::$sortOrder;
         });
         return $this->fields;
     }