diff --git a/var/Typecho/Common.php b/var/Typecho/Common.php
index 53a7b6cb..26c3e660 100644
--- a/var/Typecho/Common.php
+++ b/var/Typecho/Common.php
@@ -936,8 +936,12 @@ EOF;
      */
     public static function gravatarUrl($mail, $size, $rating, $default, $isSecure = false)
     {
-        $url = $isSecure ? 'https://secure.gravatar.com' : 'http://www.gravatar.com';
-        $url .= '/avatar/';
+        if (defined('__TYPECHO_GRAVATAR_PREFIX__')) {
+            $url = __TYPECHO_GRAVATAR_PREFIX__;
+        } else {
+            $url = $isSecure ? 'https://secure.gravatar.com' : 'http://www.gravatar.com';
+            $url .= '/avatar/';
+        }
 
         if (!empty($mail)) {
             $url .= md5(strtolower(trim($mail)));