diff --git a/wp-includes/query.php b/wp-includes/query.php
index 1e25b9ae4..f52919bfc 100644
--- a/wp-includes/query.php
+++ b/wp-includes/query.php
@@ -1503,7 +1503,7 @@ class WP_Query {
 					'operator' => 'IN'
 				);
 
-				if ( $t->rewrite['hierarchical'] ) {
+ 				if ( isset( $t->rewrite['hierarchical'] ) && $t->rewrite['hierarchical'] ) {
 					$q[$t->query_var] = wp_basename( $q[$t->query_var] );
 				}