The geometries of the thiazole ring and the nitramino groups in N-(3H-thiazol-2-ylidene)nitramine, C3H3N3O2S, (I), and N-methyl-N-(thiazol-2-yl)nitramine, C4H5N3O2S, (II), are very similar. The nitramine group in (II) is planar and twisted along the C-N bond with respect to the thiazole ring. In both structures, the asymmetric unit includes two practically equal molecules. In (I), the molecules are arranged in layers connected to each other by N-H...N and much weaker C-H...O hydrogen bonds. In the crystal structure of (II), the molecules are arranged in layers bound to each other by both weak C-H...O hydrogen bonds and S...O dipolar interactions.