Index: wp-includes/comment.php
===================================================================
--- wp-includes/comment.php	(revision 19734)
+++ wp-includes/comment.php	(working copy)
@@ -1978,7 +1978,7 @@
 	if ( empty( $posts ) || ! $query->is_singular() || ! get_option( 'close_comments_for_old_posts' ) )
 		return $posts;
 
-	$post_types = apply_filters( 'close_comments_for_post_types', array( 'post' ) );
+	$post_types = apply_filters( 'close_comments_for_post_types', array( 'post', 'attachment' ) );
 	if ( ! in_array( $posts[0]->post_type, $post_types ) )
 		return $posts;
 
@@ -2017,7 +2017,7 @@
 
 	$post = get_post($post_id);
 
-	$post_types = apply_filters( 'close_comments_for_post_types', array( 'post' ) );
+	$post_types = apply_filters( 'close_comments_for_post_types', array( 'post', 'attachment' ) );
 	if ( ! in_array( $post->post_type, $post_types ) )
 		return $open;