Index: wp-comments-post.php
===================================================================
--- wp-comments-post.php	(revision 11133)
+++ wp-comments-post.php	(working copy)
@@ -17,6 +17,8 @@
 
 nocache_headers();
 
+do_action('pre_comment_post');
+
 $comment_post_ID = (int) $_POST['comment_post_ID'];
 
 $status = $wpdb->get_row( $wpdb->prepare("SELECT post_status, comment_status FROM $wpdb->posts WHERE ID = %d", $comment_post_ID) );