--- nat_orig.module	2009-02-15 22:14:48.000000000 +0000
+++ nat.module	2009-02-16 23:38:59.000000000 +0000
@@ -570,6 +570,10 @@ function _nat_get_vocabularies() {
  *   An array of term objects.
  */
 function _nat_add_terms($vids, $title, $body, $hierarchy = array(), $relations = array(), $synonyms = NULL) {
+  if (taxonomy_get_term_by_name($title)) {
+    return array();
+  }
+
   $edit = array(
     'name' => $title,
     'description' => $body,