diff -u -r1.2.2.1 forum.install
--- modules/forum/forum.install	9 Dec 2010 22:23:56 -0000	1.2.2.1
+++ modules/forum/forum.install	20 Dec 2010 16:09:33 -0000
@@ -108,6 +108,13 @@
 function forum_update_6000() {
   $ret = array();
 
+  if (!module_exists('taxonomy')) {
+    drupal_set_message(t("Updating the Forum module requires the Taxonomy module to be enabled on the <a href=\"@admin-modules-path\">administer modules page</a>. When you enable it, you'll need to return to <a href=\"@update-php\">update.php</a> and retry updating.", array('@admin-modules-path' => url('admin/build/modules'), '@update-php' => base_path() .'update.php?op=selection')), 'warning', FALSE);
+    $query_message = t('This update could not be run because the prerequisite module Taxonomy was not enabled.');
+    $ret['#abort'] = array('success' => FALSE, 'query' => $query_message);
+    return $ret;
+  }
+
   $vid = variable_get('forum_nav_vocabulary', 0);
   $vocabularies = taxonomy_get_vocabularies();
   if (!isset($vocabularies[$vid])) {