diff --git a/inc/fields/dropdownfield.class.php b/inc/fields/dropdownfield.class.php
index 3ffc61581..8fb4c3768 100644
--- a/inc/fields/dropdownfield.class.php
+++ b/inc/fields/dropdownfield.class.php
@@ -239,7 +239,7 @@ public function displayField($canEdit = true) {
                      $itemtype::getTable(),
                      $decodedValues['show_ticket_categories_root']
                   );
-               $dparams_cond_crit['id'] = $sons;
+               $dparams_cond_crit[ItilCategory::getTable().'.id'] = $sons;
                $rootItem = new $itemtype();
                if ($rootItem->getFromDB($decodedValues['show_ticket_categories_root'])) {
                   $baseLevel = $rootItem->fields['level'];