diff --git a/library/think/Request.php b/library/think/Request.php
index dc5808d4..80546d89 100644
--- a/library/think/Request.php
+++ b/library/think/Request.php
@@ -1172,7 +1172,7 @@ class Request
     public function isAjax()
     {
         $value = $this->server('HTTP_X_REQUESTED_WITH');
-        return (!is_null($value) && strtolower($vlaue) == 'xmlhttprequest') ? true : false;
+        return (!is_null($value) && strtolower($value) == 'xmlhttprequest') ? true : false;
     }
 
     /**