diff --git a/date_admin.inc b/date_admin.inc
index 13da42e..b186fbc 100644
--- a/date_admin.inc
+++ b/date_admin.inc
@@ -596,7 +596,11 @@ function _date_field_settings_form($field, $instance, $has_data) {
  */
 function date_field_settings_validate(&$form, &$form_state) {
   $field = &$form_state['values']['field'];
+  $is_datetime = ($form_state['complete form']['#field']['type'] === 'datestamp');
 
+  if ($is_datetime && ($field['settings']['tz_handling'] === 'none')) {
+    $field['settings']['tz_handling'] = 'site';
+  }
   if ($field['settings']['tz_handling'] == 'none') {
     form_set_value($form['timezone_db'], '', $form_state);
   }
@@ -604,7 +608,7 @@ function date_field_settings_validate(&$form, &$form_state) {
     form_set_value($form['timezone_db'], date_get_timezone_db($field['settings']['tz_handling']), $form_state);
   }
 
-  if ($field['settings']['tz_handling'] != 'none' && !in_array('hour', array_filter($field['settings']['granularity']))) {
+  if (!$is_datetime && $field['settings']['tz_handling'] != 'none' && !in_array('hour', array_filter($field['settings']['granularity']))) {
     form_set_error('field[settings][tz_handling]', t('Dates without hours granularity must not use any timezone handling.'));
   }