diff --git a/wp-includes/class-wp-network.php b/wp-includes/class-wp-network.php
index d33f210dab..d835765c6b 100644
--- a/wp-includes/class-wp-network.php
+++ b/wp-includes/class-wp-network.php
@@ -307,8 +307,8 @@ class WP_Network {
 		if ( ! empty( $this->cookie_domain ) ) {
 			return;
 		}
-
-		$this->cookie_domain = $this->domain;
+		$domain              = parse_url( $this->domain, PHP_URL_HOST );
+		$this->cookie_domain = is_string( $domain ) ? $domain : $this->domain;
 		if ( str_starts_with( $this->cookie_domain, 'www.' ) ) {
 			$this->cookie_domain = substr( $this->cookie_domain, 4 );
 		}
diff --git a/wp-includes/version.php b/wp-includes/version.php
index 51a04087a3..7357831199 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '6.6-alpha-58137';
+$wp_version = '6.6-alpha-58138';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.