Posterous Importer fails due to SimpleXMLElement serialization error for ID meta

I encountered an error trying to import more than one item from Posterous.

#3 /home/altern8/workspaces/dflydev-website-wp/wp-content/plugins/posterous-importer/posterous.php(215): add_post_meta(15, 'posterous_9ba0b...', Object(SimpleXMLElement), true)

I fixed this by changing the following:

add_post_meta( $post_id, 'posterous_' . $this->bid . '_post_id', $entry->id, true );

to

add_post_meta( $post_id, 'posterous_' . $this->bid . '_post_id', (string)$entry->id, true );