The asymmetric unit of the title compound, C18H21N3S, contains five molecules. The equivalent bond distances in the five molecules are in excellent agreement, the r.m.s. fit being within 0.007 angstrom. The five molecules are linked into a chain consisting of alternating pseudo-enantiomers by N-H center dot center dot center dot S hydrogen bonds supplemented by weak C-H center dot center dot center dot pi interactions. The action of a glide plane links the asymmetric unit into an extended chain. A polymorph of the title compound with one molecule in the asymmetric unit was reported by Braun et al. [Cryst. Res. Technol. (1988), 23, 35-39].