Index: wp-includes/widgets.php
===================================================================
--- wp-includes/widgets.php	(revision 13287)
+++ wp-includes/widgets.php	(working copy)
@@ -549,8 +549,8 @@
 		'name' => sprintf(__('Sidebar %d'), $i ),
 		'id' => "sidebar-$i",
 		'description' => '',
-		'before_widget' => '<li id="%1$s" class="widget %2$s">',
-		'after_widget' => "</li>\n",
+		'before_widget' => '<ul><li id="%1$s" class="widget %2$s">',
+		'after_widget' => "</li></ul>\n",
 		'before_title' => '<h2 class="widgettitle">',
 		'after_title' => "</h2>\n",
 	);