Index: wp-includes/widgets.php
===================================================================
--- wp-includes/widgets.php	(revision 38408)
+++ wp-includes/widgets.php	(working copy)
@@ -278,14 +278,16 @@
  * Removes a sidebar from the list.
  *
  * @since 2.2.0
+ * @since x.y.0 The `$name` parameter was changed to also accept a numeric sidebar ID.
  *
  * @global array $wp_registered_sidebars Stores the new sidebar in this array by sidebar ID.
  *
- * @param string $name The ID of the sidebar when it was added.
+ * @param string|int $name The ID of the sidebar when it was registered.
  */
 function unregister_sidebar( $name ) {
 	global $wp_registered_sidebars;
 
+	$name = ( is_int($name) ) ? "sidebar-$name" : sanitize_title($name);
 	unset( $wp_registered_sidebars[ $name ] );
 }
 
@@ -302,6 +304,7 @@
 function is_registered_sidebar( $sidebar_id ) {
 	global $wp_registered_sidebars;
 
+	$sidebar_id = ( is_int($sidebar_id) ) ? "sidebar-$sidebar_id" : sanitize_title($sidebar_id);
 	return isset( $wp_registered_sidebars[ $sidebar_id ] );
 }