Required @ image issue

The option Use a graphical replacement for "@" is required which causes validation errors if not selected and checkbox_validate module is enabled.

<?php
      $form['spamspan_settings']['spamspan_use_graphic'] = array(
        '#type' => 'checkbox',
        '#title' => t('Use a graphical replacement for "@"'),
        '#default_value' => variable_get('spamspan_use_graphic', 0),
        # Drupal does not validate checkboxes natively
//        '#required' => TRUE, 
        '#description' => t('Replace "@" with a graphical representation when javascript is disabled (and ignore the setting "Replacement for @" above).')
        );
?>