Get post type and category

On my frontpage (index.php) I would like to display all posts of the type 'event' as well as the category 'main' of the type 'post'. How can I merge those two conditions? In my current code, I can filter the two post-types but not the category 'main'.

<?php global $wp_query; $args = array_merge( $wp_query->query, array( 'post_type' => array('post','event') ));
query_posts( $args ); ?>

Just change the $args to this:

<?php
$args = array(
    'post_type' => array('post','event'),

    'tax_query' => array(
          'relation' => 'OR',
       array(
         'taxonomy' => 'category',
         'terms' => 'main',
         'field' => 'slug'
       ),
       array(
         'taxonomy' => 'event_tag', // this needs to be whatever custom taxonomy you have declared for your custom post type.
         'terms' => 'main',
         'field' => 'slug'
       ),
    )
);
?>