diff --git a/wp-includes/classes.php b/wp-includes/classes.php
index b1c117c041..960e9b2ac8 100644
--- a/wp-includes/classes.php
+++ b/wp-includes/classes.php
@@ -1162,7 +1162,7 @@ class Walker_Page extends Walker {
 		$css_class = 'page_item page-item-'.$page->ID;
 		if ( !empty($current_page) ) {
 			$_current_page = get_page( $current_page );
-			if ( in_array($page->ID, (array) $_current_page->ancestors) )
+			if ( isset($_current_page->ancestors) && in_array($page->ID, (array) $_current_page->ancestors) )
 				$css_class .= ' current_page_ancestor';
 			if ( $page->ID == $current_page )
 				$css_class .= ' current_page_item';