A fourth polymorph of the 4-chloro-1,2,3,5-dithiadiazolyl radical, ClCNSSN is reported. It crystallises as twisted cofacial dimers in the triclinic space group P-1 with four molecules in the asymmetric unit. Whilst the structure exhibits three-centre SSδ+ Nδ− motifs similar to those previously observed in the α, β and γ phases, only 75% of the anticipated number of contacts are observed.