diff --git a/wp-includes/rewrite.php b/wp-includes/rewrite.php
index 33bc4d61b1..dde1b1810b 100644
--- a/wp-includes/rewrite.php
+++ b/wp-includes/rewrite.php
@@ -185,6 +185,7 @@ class WP_Rewrite {
 	var $extra_rules = array(); //those not generated by the class, see add_rewrite_rule()
 	var $extra_rules_top = array(); //those not generated by the class, see add_rewrite_rule()
 	var $non_wp_rules = array(); //rules that don't redirect to WP's index.php
+	var $extra_permastructs = array();
 	var $endpoints;
 	var $use_verbose_rules = false;
 	var $use_verbose_page_rules = true;