diff --git a/wp-includes/classes.php b/wp-includes/classes.php
index 9efe55ee8c..f2f3561a6d 100644
--- a/wp-includes/classes.php
+++ b/wp-includes/classes.php
@@ -551,7 +551,7 @@ class Walker_Page extends Walker {
 		extract($args, EXTR_SKIP);
 		$css_class = 'page_item page-item-'.$page->ID;
 		$_current_page = get_page( $current_page );
-		if ( in_array($page->ID, $_current_page->ancestors) )
+		if ( in_array($page->ID, (array) $_current_page->ancestors) )
 			$css_class .= ' current_page_ancestor';
 		if ( $page->ID == $current_page )
 			$css_class .= ' current_page_item';