  We show that the Satake-Baily-Borel compactification of the moduli space of
lattice polarized K3 surfaces parametrizing K3 surfaces of degree 2 with four
rational double points of type $D_4$ is the projective 3-space. We also show
that the corresponding graded ring of automorphic forms is generated by four
elements of weight 2 and one element of weight 11 with one relation of weight
22.
