The classical Lattice Boltzmann Method is based on an orthogonal, equidistant lattice structure. Thus, representation of non-rectangular boundaries deserves further attention. Besides the straightforward possibility of representing a non-rectangular boundary by a staircase, there are more sophisticated approaches in the literature for an accurate modelling of a non-rectangular boundary. In the present paper, three such methods arc compared with each other, and with the straightforward staircase approximation on two laminar flow test cases. As the reference solution, results obtained by a commercial CFD code are used, which are obtained by an exact representation of the non-orthogonal boundaries, using non-orthogonal finite volume discretisation. The results show that the so-called extrapolation method's performance is slightly inferior compared to the other methods; however, all methods exhibit a comparable overall accuracy.