I followed the next docs regarding a custom error page. I want to reuse the error page if certain errors occur at getStaticProps. Something like:

const Page: NextPage<Props> = ({ pageData, error }: Props) => {
  if (error) return <Error statusCode={500} />;
  return <Page data={pageData} />;
};

export const getStaticProps: GetStaticProps = async ({
  params,
}: {
  params: { [prop: string]: string[] };
}) => {
  const { slug } = params;
  const {pageData, error} = getPageData(slug)

  return {
    props: {
      pageData: page || null,
      error: error || null,
    },
  };
};

export default Page;

The error page is just like in the docs:

function Error({ statusCode }) {
  return (
    <p>
      {statusCode ? `An error ${statusCode} occurred on server` : 'An error occurred on client'}
    </p>
  );
}

Error.getInitialProps = ({ res, err }) => {
  const statusCode = res ? res.statusCode : err ? err.statusCode : 404;
  return { statusCode };
};

export default Error;

This works but the status code ist wrong. Nextjs still answers a request to this page with a status code 200. I need it to set the status code to 500 as if there was a server error.