The title mol-ecule, C(15)H(21)N(3)S, exists as the thione tautomer in the solid state. The 1,2,4-triazole ring is almost planar (r.m.s. deviation = 0.004 Å) and the prop-2-en-1-yl chain is close to being perpendicular to this plane [C-N-C-C torsion angle = 77.1 (5)°]. In the crystal, centrosymmetric dimeric aggregates are formed by pairs of N-H⋯S hydrogen bonds as parts of eight-membered (⋯HNCS)(2) synthons. These are connected into layers parallel to (101) via C-H⋯π inter-actions, where the π-system is the triazole ring. The investigated sample was a nonmerohedral twin; the refined domain ratio was 0.655 (4):0.345 (4).