Gutenberg – editor-font-sizes in functions not working

I believe to get this working I wasn’t calling this at the correct time, and I wrapped it in a function after_setup_theme, like so:

add_action( 'after_setup_theme', 'ttp_custom_font_sizes' );

function ttp_custom_font_sizes() {

  // removes custom font sizes
  add_theme_support('disable-custom-font-sizes');

  // add my own custom sizes 
  add_theme_support( 'editor-font-sizes', array(
    array(
        'name' => __( 'Small'),
        'size' => 12,
        'slug' => 'small'
    ),
    array(
        'name' => __( 'Normal'),
        'size' => 16,
        'slug' => 'normal'
    ),
    array(
        'name' => __( 'Large'),
        'size' => 36,
        'slug' => 'large'
    ),
    array(
        'name' => __( 'Huge'),
        'size' => 50,
        'slug' => 'huge'
    )
    ) );
}