Custom taxonomy / show in editor

Hi there,

I'm using a CPT called "chat" that comes with a chat-category (custom taxonomy). Unfortunately, the category is missing in the settings menu of the WP editor ;-(

The agrs of the chat category are as follows:

$args = array(
	'labels'                     => $labels,
	'hierarchical'               => true,
	'public'                     => true,
	'show_ui'                    => true,
	'show_admin_column'          => true,
	'show_in_nav_menus'          => true,
	'show_tagcloud'              => false,
);

What is the missing to make the category show up in the settings also?

Thanks,
Jan