diff --git a/plugins/kolab_files/lib/kolab_files_engine.php b/plugins/kolab_files/lib/kolab_files_engine.php
index 6e81e1ad..8cb408bd 100644
--- a/plugins/kolab_files/lib/kolab_files_engine.php
+++ b/plugins/kolab_files/lib/kolab_files_engine.php
@@ -34,7 +34,7 @@ class kolab_files_engine
      */
     public function __construct($plugin, $url)
     {
-        $this->url    = $this->resolve_url($url);
+        $this->url    = rcube_utils::resolve_url($url);
         $this->plugin = $plugin;
         $this->rc     = $plugin->rc;
     }
@@ -1017,30 +1017,4 @@ class kolab_files_engine
 
         return $mimetypes;
     }
-
-    /**
-     * Resolve relative URL
-     */
-    protected function resolve_url($url)
-    {
-        // prepend protocol://hostname:port
-        if (!preg_match('|^https?://|', $url)) {
-            $schema       = 'http';
-            $default_port = 80;
-
-            if (rcube_utils::https_check()) {
-                $schema       = 'https';
-                $default_port = 443;
-            }
-
-            $prefix = $schema . '://' . preg_replace('/:\d+$/', '', $_SERVER['HTTP_HOST']);
-            if ($_SERVER['SERVER_PORT'] != $default_port) {
-                $prefix .= ':' . $_SERVER['SERVER_PORT'];
-            }
-
-            $url = $prefix . ($url[0] == '/' ? '' : '/') . $url;
-        }
-
-        return $url;
-    }
 }