diff --git a/modules/forum.module b/modules/forum.module
index 7e36b4087d69732feba006c0ca9c13928eae77f6..3aae6b469050c8dfed0798c0441e3609a2548f4c 100644
--- a/modules/forum.module
+++ b/modules/forum.module
@@ -587,11 +587,7 @@ function forum_update($node) {
 function forum_form(&$node) {
   $form['title'] = array('#type' => 'textfield', '#title' => t('Subject'), '#default_value' => $node->title, '#required' => TRUE);
 
-  if (!$node->nid) {
-    // new topic
-    $node->taxonomy[] = arg(3);
-  }
-  else {
+  if ($node->nid) {
     $forum_terms = taxonomy_node_get_terms_by_vocabulary(_forum_get_vid(), $node->nid);
     // if editing, give option to leave shadows
     $shadow = (count($forum_terms) > 1);
@@ -605,6 +601,16 @@ function forum_form(&$node) {
   return $form;
 }
 
+/**
+ * Implementation of hook_prepare; assign forum taxonomy when adding a topic from within a forum.
+ */
+function forum_prepare(&$node) {
+  if (!$node->nid) {
+    // new topic
+    $node->taxonomy[] = arg(3);
+  }
+}
+
 /**
  * Implementation of hook_insert().
  */
diff --git a/modules/forum/forum.module b/modules/forum/forum.module
index 7e36b4087d69732feba006c0ca9c13928eae77f6..3aae6b469050c8dfed0798c0441e3609a2548f4c 100644
--- a/modules/forum/forum.module
+++ b/modules/forum/forum.module
@@ -587,11 +587,7 @@ function forum_update($node) {
 function forum_form(&$node) {
   $form['title'] = array('#type' => 'textfield', '#title' => t('Subject'), '#default_value' => $node->title, '#required' => TRUE);
 
-  if (!$node->nid) {
-    // new topic
-    $node->taxonomy[] = arg(3);
-  }
-  else {
+  if ($node->nid) {
     $forum_terms = taxonomy_node_get_terms_by_vocabulary(_forum_get_vid(), $node->nid);
     // if editing, give option to leave shadows
     $shadow = (count($forum_terms) > 1);
@@ -605,6 +601,16 @@ function forum_form(&$node) {
   return $form;
 }
 
+/**
+ * Implementation of hook_prepare; assign forum taxonomy when adding a topic from within a forum.
+ */
+function forum_prepare(&$node) {
+  if (!$node->nid) {
+    // new topic
+    $node->taxonomy[] = arg(3);
+  }
+}
+
 /**
  * Implementation of hook_insert().
  */