diff --git a/modules/forum.module b/modules/forum.module
index cbc3034a3fc..6391233e1b6 100644
--- a/modules/forum.module
+++ b/modules/forum.module
@@ -214,7 +214,7 @@ function forum_validate(&$node) {
 }
 
 function forum_form(&$node, &$error) {
-  if (!$node->taxonomy) {
+  if (!$node->nid) {
     // new topic
     $node->taxonomy[] = arg(3);
   }
diff --git a/modules/forum/forum.module b/modules/forum/forum.module
index cbc3034a3fc..6391233e1b6 100644
--- a/modules/forum/forum.module
+++ b/modules/forum/forum.module
@@ -214,7 +214,7 @@ function forum_validate(&$node) {
 }
 
 function forum_form(&$node, &$error) {
-  if (!$node->taxonomy) {
+  if (!$node->nid) {
     // new topic
     $node->taxonomy[] = arg(3);
   }