Filter post_meta in WordPress searches

functions.php

<?php
  add_filter('pre_get_posts','klausk_search_meta');
  function klausk_search_meta($q=false){
    if (!is_admin() && $q->is_main_query() && $q->is_search()) {
      $meta_query = array(
        array(
          'key' => 'klausk_answer',
          'value' => like_escape($q->get('s')),
          'compare' => 'LIKE',
        ),
      );
      $q->set('meta_query',$meta_query);
    }
    return $q;
  }
?>