diff --git a/hms_field.module b/hms_field.module
index bc8efe6..338f3ca 100644
--- a/hms_field.module
+++ b/hms_field.module
@@ -568,7 +568,7 @@ function _add_multi_search_tokens($item) {
 /**
  * Helper function to convert input values to seconds (FORM API).
  */
-function _hms_value_callback($element, $input = NULL, $form_state) {
+function _hms_value_callback($element, $input, $form_state) {
   if ($form_state['process_input'] && (!empty($input) || $input === 0)) {
     return _hms_formatted_to_seconds($input, $element['#format']);
   }
@@ -599,4 +599,3 @@ function _hms_add_running_js() {
   drupal_add_js(drupal_get_path('module', 'hms_field') . '/hms_field.js');
   drupal_add_js(array('hms_field' => array('servertime' => REQUEST_TIME, 'factor_map' => _hms_factor_map())), 'setting');
 }
-