Index: wp-includes/bookmark-template.php
===================================================================
--- wp-includes/bookmark-template.php	(revision 23294)
+++ wp-includes/bookmark-template.php	(working copy)
@@ -214,6 +214,11 @@
 
 	$output = '';
 
+	if ( ! is_array( $class ) )
+		$class = explode( ' ', $class );
+	$class = array_map( 'sanitize_html_class', $class );
+	$class = trim( join( ' ', $class ) );
+
 	if ( $categorize ) {
 		$cats = get_terms( 'link_category', array( 'name__like' => $category_name, 'include' => $category, 'exclude' => $exclude_category, 'orderby' => $category_orderby, 'order' => $category_order, 'hierarchical' => 0 ) );
 		if ( empty( $cats ) )