diff --git a/modules/taxonomy_node/taxonomynode.module b/modules/taxonomy_node/taxonomynode.module
index d30d5dc..0885b0c 100644
--- a/modules/taxonomy_node/taxonomynode.module
+++ b/modules/taxonomy_node/taxonomynode.module
@@ -270,12 +270,12 @@ function taxonomynode_form_alter(&$form, &$form_state, $form_id) {
   }
 
   if (substr($form_id, -10) == '_node_form') {
-    $nid = $form['nid']['#value'];
     // find vid in module table
-    if ($nid) {
+    if (!empty($form['nid']['#value'])) {
+      $nid = $form['nid']['#value'];
       $row = db_fetch_object(db_query("SELECT * FROM {taxonomynode} tn WHERE tn.nid = %d", $nid));
-      $vid = $row->vid;
-      if ($vid) {
+      if (!empty($row->vid)) {
+        $vid = $row->vid;
         $vocab = taxonomy_vocabulary_load($vid);
         $form['taxonomy'][$vid .'_disabled'] = $form['taxonomy'][$vid];
         $form['taxonomy'][$vid .'_disabled']['#multiple'] = ($vocab->hierarchy == 2);