diff --git a/wp-includes/ms-default-constants.php b/wp-includes/ms-default-constants.php
index 7d794e32e6..016ed437b7 100644
--- a/wp-includes/ms-default-constants.php
+++ b/wp-includes/ms-default-constants.php
@@ -68,7 +68,8 @@ function ms_cookie_constants() {
 	 * @since 2.6.0
 	 */
 	if ( ! defined( 'ADMIN_COOKIE_PATH' ) ) {
-		if ( ! is_subdomain_install() || trim( parse_url( get_option( 'siteurl' ), PHP_URL_PATH ), '/' ) ) {
+		$site_path = parse_url( get_option( 'siteurl' ), PHP_URL_PATH );
+		if ( ! is_subdomain_install() || is_string( $site_path ) && trim( $site_path, '/' ) ) {
 			define( 'ADMIN_COOKIE_PATH', SITECOOKIEPATH );
 		} else {
 			define( 'ADMIN_COOKIE_PATH', SITECOOKIEPATH . 'wp-admin' );
diff --git a/wp-includes/version.php b/wp-includes/version.php
index d8b5addf4d..f775a98ac4 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.9-alpha-51629';
+$wp_version = '5.9-alpha-51630';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.