diff --git a/nag/lib/Nag.php b/nag/lib/Nag.php
index f66e281b834..0f05253efe9 100644
--- a/nag/lib/Nag.php
+++ b/nag/lib/Nag.php
@@ -1535,10 +1535,10 @@ static public function _rsortByEstimate($a, $b)
      */
     static public function _sortByDue($a, $b)
     {
-        $a_due = empty($a->due)
+        $a_due = empty($a->getNextDue())
             ? 0
             : $a->getNextDue()->timestamp();
-        $b_due = empty($b->due)
+        $b_due = empty($b->getNextDue())
             ? 0
             : $b->getNextDue()->timestamp();