Reorder products by SKU

I’m trying to get the default product display to be sorted by the sku field in ascending order. So far I’ve come up with this:

/* Order products by SKU */
function reorder_products_by_sku( $query ) {
	if(is_shop() && ! is_admin() && $query->is_main_query()) {
		$query->set('orderby', 'meta_value_num');
		$query->set('meta_key', 'sku');
		$query->set('order', 'ASC');
	}
}
add_action( 'pre_get_posts', 'reorder_products_by_sku' );

This just tells me there are no products found which match my selection. Can anyone point me towards what I’m doing wrong?

Thanks

https://www.ads-software.com/extend/plugins/woocommerce/