Index: wp-includes/post.php
===================================================================
--- wp-includes/post.php	(revision 8674)
+++ wp-includes/post.php	(working copy)
@@ -3297,7 +3297,7 @@
 	if ( !$post || empty($post['ID']) )
 		return;
 
-	if ( isset($post['post_type']) && 'revision' == $post_post['type'] )
+	if ( isset($post['post_type']) && 'revision' == $post['post_type'] )
 		return new WP_Error( 'post_type', __( 'Cannot create a revision of a revision' ) );
 
 	$post = _wp_post_revision_fields( $post, $autosave );