Update from 6.x-1.2-beta1 to beta7 fails with postgresql

In themekey_ui.install is a query that fails with postgresql on line 58:
$sql = "SELECT id, value, theme, nid, vid FROM {themekey_properties} JOIN {node_revisions} ON (value = nid) WHERE property = 'node:nid' AND conditions = '%s'";

Error message:
pg_query() [http://www.php.net/manual/en/function.pg-query.php]: Query failed: ERROR: operator does not exist: character varying = int_unsigned LINE 1: ...themekey_properties JOIN node_revisions ON (value = nid) WHE... ^ HINT: No operator matches the given name and argument type(s). You might need to add explicit type casts.

Can be solved for postgresql with an explicit type cast like:
$sql = "SELECT id, value, theme, nid, vid FROM {themekey_properties} JOIN {node_revisions} ON (value = nid::character varying) WHERE property = 'node:nid' AND conditions = '%s'";

But I don't know yet how casts are generally handled in drupal.