diff --git a/aegir/conf/global.inc b/aegir/conf/global.inc
index 5a6603dc8..f4ef63a29 100644
--- a/aegir/conf/global.inc
+++ b/aegir/conf/global.inc
@@ -829,9 +829,12 @@ if (!$is_backend && isset($_SERVER['HTTP_HOST']) &&
     header("X-Site-Subdir: " . $site_subdir);
   }
 
-  if ($all_ini['server_name_cookie_domain'] || $site_subdir) {
+  if ($all_ini['server_name_cookie_domain']) {
     $domain = '.' . preg_replace('`^www\.`', '', $_SERVER['SERVER_NAME']);
   }
+  elseif ($site_subdir && isset($_SERVER['RAW_HOST'])) {
+    $domain = '.' . preg_replace('`^www\.`', '', $_SERVER['RAW_HOST']);
+  }
   else {
     $domain = '.' . preg_replace('`^www\.`', '', $_SERVER['HTTP_HOST']);
   }