diff --git advancedbookblocks.module advancedbookblocks.module
index b3399b0..0f273f9 100644
--- advancedbookblocks.module
+++ advancedbookblocks.module
@@ -484,6 +484,7 @@ function books_get_top_level($d = NULL, $context = NULL) {
 }
 
 function get_book_children($mlid) {
+  $nid_array = array();
   $result = db_query(db_rewrite_sql("SELECT mlid, weight, link_title FROM {menu_links} ml WHERE ml.plid = %d ORDER by weight, link_title", "ml", "mlid"), $mlid);
   while ($child = db_fetch_object($result)) {
     if (!empty($child->mlid)) {