Next / Previous Post Link PHP Error

I guess I’ll answer my own question again. For anyone’s future reference on how to get next_post_link to work with custom post types, just stick this in the theme’s functions.php file:

<?php
	function get_custom_adjacent_post_join($join, $in_same_cat) {
		global $post, $wpdb;

		// we don't process empty post and default post types
		if (empty($post) || in_array($post->post_type, array('post', 'page', 'attachment', 'revision', 'nav_menu_item')))
			return $join;

		// here we specify custom post types and their corresponding taxonomies
		$taxonomies = array(
			'your_custom_post_type'	=> 'your_taxonomy'
		);

		$current_taxonomy = $taxonomies[$post->post_type];

		if ($in_same_cat) {
		$join = " INNER JOIN $wpdb->term_relationships AS tr ON p.ID = tr.object_id INNER JOIN $wpdb->term_taxonomy tt ON tr.term_taxonomy_id = tt.term_taxonomy_id";

		if ( $in_same_cat ) {
			$cat_array = wp_get_object_terms($post->ID, $current_taxonomy, array('fields' => 'ids'));
			$join .= " AND tt.taxonomy = '$current_taxonomy' AND tt.term_id IN (" . implode(',', $cat_array) . ")";
		}
		}
		return $join;
	}
	add_filter('get_previous_post_join', 'get_custom_adjacent_post_join', 10, 2);
	add_filter('get_next_post_join', 'get_custom_adjacent_post_join', 10, 2);
	?>