function wc_increase_stock_levels( $order_id ) {
	if ( is_a( $order_id, 'WC_Order' ) ) {
		$order    = $order_id;
		$order_id = $order->get_id();
	} else {
		$order = wc_get_order( $order_id );
	}

	// We need an order, and a store with stock management to continue.
	if ( ! $order || 'yes' !== get_option( 'woocommerce_manage_stock' ) || ! apply_filters( 'woocommerce_can_restore_order_stock', true, $order ) ) {
		return;
	}

	$changes = array();

	// Loop over all items.
	foreach ( $order->get_items() as $item ) {
		if ( ! $item->is_type( 'line_item' ) ) {
			continue;
		}

		// Only increase stock once for each item.
		$product            = $item->get_product();
		$item_stock_reduced = $item->get_meta( '_reduced_stock', true );

		if ( ! $item_stock_reduced || ! $product || ! $product->managing_stock() ) {
			continue;
		}

		$item_name = $product->get_formatted_name();
		$new_stock = wc_update_product_stock( $product, $item_stock_reduced, 'increase' );

		if ( is_wp_error( $new_stock ) ) {
			/* translators: %s item name. */
			$order->add_order_note( sprintf( __( 'Unable to restore stock for item %s.', 'woocommerce' ), $item_name ) );
			continue;
		}

		$item->delete_meta_data( '_reduced_stock' );
		$item->save();

		$changes[] = $item_name . ' ' . ( $new_stock - $item_stock_reduced ) . '→' . $new_stock;
	}

	if ( $changes ) {
		$order->add_order_note( __( 'Stock levels increased:', 'woocommerce' ) . ' ' . implode( ', ', $changes ) );
	}

	do_action( 'woocommerce_restore_order_stock', $order );
}