Taxonomy in custom post types

Greetings all. I am trying to use the “Post Tags” taxonomy in a custom post type that I made, however it’s not showing up. I have tried 2 things so far. First I added it to the Taxonomies option under register_post_type. I then tried to add it using register_taxonomy_for_object_type but that didn’t work either. Here is the code I’m currently using:

register_post_type('game', array(
	'label' => __('Games'),
	'singular_label' => __('Game'),
	'public' => true,
	'publicly_queryable' => true,
	'show_ui' => true,
	'capability_type' => 'post',
	'_builtin' => false,
	'supports' => array('title', 'editor', 'thumbnail'),
	'query_var' => 'game',
	'taxonomies' => array('developer', 'genre', 'post_tag'),
	'rewrite' => array("slug" => "game")
));

Any help would be greatly appreciated. If any other information is needed please let me know.