diff --git a/lib/drivers/seafile/seafile_api.php b/lib/drivers/seafile/seafile_api.php
--- a/lib/drivers/seafile/seafile_api.php
+++ b/lib/drivers/seafile/seafile_api.php
@@ -115,9 +115,6 @@
      */
     public static function http_request($config = array())
     {
-        // load HTTP_Request2
-        require_once 'HTTP/Request2.php';
-
         // remove unknown config, otherwise HTTP_Request will throw an error
         $config = array_intersect_key($config, array_flip(array(
             'connect_timeout', 'timeout', 'use_brackets', 'protocol_version',
diff --git a/lib/file_manticore_api.php b/lib/file_manticore_api.php
--- a/lib/file_manticore_api.php
+++ b/lib/file_manticore_api.php
@@ -59,8 +59,6 @@
      */
     public function __construct($base_url)
     {
-        require_once 'HTTP/Request2.php';
-
         $config         = rcube::get_instance()->config;
         $this->debug    = rcube_utils::get_boolean($config->get('fileapi_manticore_debug'));
         $this->base_url = rtrim($base_url, '/') . '/';
diff --git a/lib/file_ui_api.php b/lib/file_ui_api.php
--- a/lib/file_ui_api.php
+++ b/lib/file_ui_api.php
@@ -58,7 +58,6 @@
      */
     public function init()
     {
-        require_once 'HTTP/Request2.php';
         $this->request = new HTTP_Request2();
         self::configure($this->request);
     }
diff --git a/lib/file_wopi.php b/lib/file_wopi.php
--- a/lib/file_wopi.php
+++ b/lib/file_wopi.php
@@ -237,8 +237,6 @@
      */
     protected function http_request()
     {
-        require_once 'HTTP/Request2.php';
-
         $request = new HTTP_Request2();
 
         // Configure connection options