diff --git a/inc/field/dropdownfield.class.php b/inc/field/dropdownfield.class.php
index c9831bac9..bb7a35516 100644
--- a/inc/field/dropdownfield.class.php
+++ b/inc/field/dropdownfield.class.php
@@ -315,7 +315,7 @@ public function buildParams($rand = null) {
             $itemtype::getTable(),
             $decodedValues['show_ticket_categories_root']
          );
-         $dparams_cond_crit['id'] = $sons;
+         $dparams_cond_crit[$itemtype::getTable() . '.id'] = $sons;
          $rootItem = new $itemtype();
          if ($rootItem->getFromDB($decodedValues['show_ticket_categories_root'])) {
             $baseLevel = $rootItem->fields['level'];