How do you add headers to a response with a middleware?

I can't figure out how to how to add headers to a response from a middleware. I've used both ->header(...) and ->headers->set(...) but both gives errors. So how do you do it?

First I tried with

public function handle($request, Closure $next) {
    $response = $next($request);

    $response->headers->set('refresh', '5;url=' . route('foo'));

    return $response;
}

which is the same as in Illuminate\Http\Middleware\FrameGuard.php, but that gives

Call to a member function set() on a non-object

Second I tried with

public function handle($request, Closure $next) {
    $response = $next($request);

    $response->header('refresh', '5;url=' . route('foo'));

    return $response;
}

But that gives

Method [header] does not exist on view.

So how do you add headers from a middleware?

I solved this by using the response helper.

use Illuminate\Http\RedirectResponse;

$response = $next($request);
$response = $response instanceof RedirectResponse ? $response : response($response);

return $response->header('refresh', '5;url=' . route('foo'));

All my other middleware seems to run fine with this so I guess it's fine.