Extending my own controller in Symfony

I am creating a webapp that has some common functions. So I figured the easiest way to do this would be to make a base controller and just extend that. So in the base controller I have (similar to):

namespace AppBundle\Controller;

use Sensio\Bundle\FrameworkExtraBundle\Configuration\Route;
use Symfony\Bundle\FrameworkBundle\Controller\Controller;
use Symfony\Component\HttpFoundation\Request;

class BaseController extends Controller
{
    protected function dosomething($data)
    {
        return $data;
    }
}

And then in the default controller:

namespace AppBundle\Controller;

use Sensio\Bundle\FrameworkExtraBundle\Configuration\Route;
use Symfony\Bundle\FrameworkBundle\Controller\Controller;
use Symfony\Component\HttpFoundation\Request;

class DefaultController extends BaseController
{
    /**
     * @Route("/", name="homepage")
     */
    public function indexAction()
    {
        $data = "OK";
        $thedata = $this->dosomething($data);
    }
}

And then for the Admin Controller: namespace AppBundle\Controller;

use Sensio\Bundle\FrameworkExtraBundle\Configuration\Route;
use Symfony\Bundle\FrameworkBundle\Controller\Controller;
use Symfony\Component\HttpFoundation\Request;

class AdminController extends BaseController
{
    /**
     * @Route("/", name="homepage")
     */
    public function indexAction()
    {
        $data = "OK";
        $thedata = $this->dosomething($data);
    }
}

However, I am getting errors like "Compile Error: Access level to AppBundle\Controller\AdminController::dosomething() must be protected (as in class AppBundle\Controller\BaseController) or weaker", not just when I load the admin controller function, but default as well. When I stop the admin controller extending base controller, this error goes (seems to work on default but not admin).

I'm guessing somewhere I have to let Symfony know that the admin controller is safe or something?