diff --git a/inc/fields/dropdownfield.class.php b/inc/fields/dropdownfield.class.php
index e192e1bb8..9b166d5b5 100644
--- a/inc/fields/dropdownfield.class.php
+++ b/inc/fields/dropdownfield.class.php
@@ -230,7 +230,11 @@ public static function getName() {
    public function isValid() {
       // If the field is required it can't be empty
       $itemtype = json_decode($this->fields['values'], true);
-      $itemtype = $itemtype['itemtype'];
+      if ($itemtype === null) {
+         $itemtype = $this->fields['values'];
+      } else {
+         $itemtype = $itemtype['itemtype'];
+      }
       $dropdown = new $itemtype();
       if ($this->isRequired() && $dropdown->isNewId($this->value)) {
          Session::addMessageAfterRedirect(