Index: src/wp-includes/widgets/class-wp-widget-links.php
===================================================================
--- src/wp-includes/widgets/class-wp-widget-links.php	(revision 42349)
+++ src/wp-includes/widgets/class-wp-widget-links.php	(working copy)
@@ -48,7 +48,7 @@
 		$order            = $orderby == 'rating' ? 'DESC' : 'ASC';
 		$limit            = isset( $instance['limit'] ) ? $instance['limit'] : -1;
 
-		$before_widget = preg_replace( '/id="[^"]*"/', 'id="%id"', $args['before_widget'] );
+		$before_widget = preg_replace( '/ id="[^"]*"/', ' id="%id"', $args['before_widget'] );
 
 		$widget_links_args = array(
 			'title_before'     => $args['before_title'],