Index: wp-includes/comment-template.php
===================================================================
--- wp-includes/comment-template.php	(revision 23399)
+++ wp-includes/comment-template.php	(working copy)
@@ -773,7 +773,7 @@
 
 	$_post = get_post($post_id);
 
-	$open = ( 'open' == $_post->comment_status );
+	$open = ( null != $_post && 'open' == $_post->comment_status );
 	return apply_filters( 'comments_open', $open, $post_id );
 }