diff --git a/mod/resource/type/file/resource.class.php b/mod/resource/type/file/resource.class.php
index 30eb00554a2..7c87efe4f46 100644
--- a/mod/resource/type/file/resource.class.php
+++ b/mod/resource/type/file/resource.class.php
@@ -789,8 +789,9 @@ class resource_file extends resource_base {
 
         $this->set_parameters(); // set the parameter array for the form
 
-        $mform->addElement('choosecoursefile', 'reference', get_string('location'));
+        $mform->addElement('choosecoursefile', 'reference', get_string('location'), null, array('maxlength' => 255, 'size' => 48));
         $mform->setDefault('reference', $CFG->resource_defaulturl);
+        $mform->addGroupRule('reference', array('value' => array(array(get_string('maximumchars', '', 255), 'maxlength', 255, 'client'))));
         $mform->addRule('name', null, 'required', null, 'client');
 
         if (!empty($CFG->resource_websearch)) {