The title compound, C7H4S3, is crystallizes in the monoclinic space group P21/n; it is the second polymorph, the first having been reported recently in space group C2/c [Boukebbous et al. (2016) IUCrData, 1, x161688]. The molecule displays an almost planar geometry with two fused rings [S10—C3—C4—C9 torsion angle = 0.2 (5)°]. In the crystal, short S...S [3.555 (1) and 3.503 (1) Å] contacts and π–π aromatic stacking [shortest centroid–centroid separation = 4.006 (5) Å] sustain the three-dimensional molecular packing.