Index: wp-includes/comment.php
===================================================================
--- wp-includes/comment.php	(revision 29625)
+++ wp-includes/comment.php	(working copy)
@@ -511,7 +511,10 @@
 		if ( $groupby ) {
 			$groupby = 'GROUP BY ' . $groupby;
 		}
-		$query = "SELECT $fields FROM $wpdb->comments $join WHERE $where $groupby ORDER BY $orderby $order $limits";
+		if ( $orderby ) {
+			$orderby = 'ORDER BY ' . $orderby;
+		}
+		$query = "SELECT $fields FROM $wpdb->comments $join WHERE $where $groupby $orderby $order $limits";
 
 		if ( $this->query_vars['count'] ) {
 			return $wpdb->get_var( $query );