--- modules/book/book.module.orig	2008-05-07 12:07:17.000000000 +0200
+++ modules/book/book.module	2008-05-07 12:09:05.000000000 +0200
@@ -428,7 +428,9 @@ function book_content($node, $teaser = F
 function book_nodeapi(&$node, $op, $teaser, $page) {
   switch ($op) {
     case 'load':
-      return db_fetch_array(db_query('SELECT parent, weight FROM {book} WHERE vid = %d', $node->vid));
+      if ($node->type == 'book') {
+        return db_fetch_array(db_query('SELECT parent, weight FROM {book} WHERE vid = %d', $node->vid));
+      }
       break;
     case 'view':
       if (!$teaser) {