diff --git a/wp-includes/ms-default-constants.php b/wp-includes/ms-default-constants.php
index ac3e612f0..23e04f3c4 100644
--- a/wp-includes/ms-default-constants.php
+++ b/wp-includes/ms-default-constants.php
@@ -63,8 +63,8 @@ function ms_cookie_constants(  ) {
 	/**
 	 * @since 2.0.0
 	 */
-	if ( !defined('COOKIE_DOMAIN') && 'localhost' != $current_site->domain ) {
-		if ( isset( $current_site->cookie_domain ) )
+	if ( !defined('COOKIE_DOMAIN') && is_subdomain_install() ) {
+		if ( !empty( $current_site->cookie_domain ) )
 			define('COOKIE_DOMAIN', '.' . $current_site->cookie_domain);
 		else
 			define('COOKIE_DOMAIN', '.' . $current_site->domain);