Index: modules/forum/forum.module
===================================================================
RCS file: /cvs/drupal/drupal/modules/forum/forum.module,v
retrieving revision 1.438
diff -u -r1.438 forum.module
--- modules/forum/forum.module	20 Dec 2007 21:43:01 -0000	1.438
+++ modules/forum/forum.module	21 Dec 2007 12:28:17 -0000
@@ -258,7 +258,7 @@
       break;
 
     case 'update':
-      if (!$node->revision && db_result(db_query('SELECT tid FROM {forum} WHERE nid=%d', $node->nid))) {
+      if (empty($node->revision) && db_result(db_query('SELECT tid FROM {forum} WHERE nid=%d', $node->nid))) {
         if (!empty($node->tid)) {
           db_query('UPDATE {forum} SET tid = %d WHERE vid = %d', $node->tid, $node->vid);
         }