Drupal core search and Premium module

It seems like Drupal search doesn't index content of premium nodes. Can anyone give me an advice how to fix this ?

I tried the following:

<?php
/**
 * Implementation of hook_nodeapi().
 */
function MYMODULE_nodeapi(&$node, $op, $a3 = NULL, $a4 = NULL) {
  if ($op == 'update index') {
    return $node->content['body']['#value'];
  }
}
?>

but unfortunately it didn't help.

Thanks.