diff --git a/src/Url.php b/src/Url.php
index df415ad..34bf8da 100644
--- a/src/Url.php
+++ b/src/Url.php
@@ -68,7 +68,7 @@ protected function parseUrl(string $url, &$domain): string
         return $url;
     }
 
-    public function build()
+    public function build(): string
     {
         // 解析URL
         $url     = $this->url;