Magnetic hyperfine fields transferred at Sn-119 probe atoms (in both Sn(II) and Sn(IV) valence states) in antiferromagnetic alpha-MnS have been for the first time investigated. At 6 K, a unique hyperfine splitting pattern (H = 27 kOe) was observed for the Sn(II) substituant, isovalent with Mn(II), and two for the Sn(IV) heterovalent substituant (H-1 = 392 kOe and H-2 = 296 kOe). The charge compensation mechanism is shown to mainly involve Mn(II) vacancy location in the vicinity of Sn(IV), the two magnetically non-equivalent surroundings of Sn(IV) being related to the two possible spin orientations of the missing nearest neighbor Mn(II). The large difference in H values observed for Sn(II) and Sn(IV) is interpreted as an indication of the prevalent contribution of 3d-5s transfer in the spin polarization of the diamagnetic impurity. The Mossbauer lattice temperature for the Sn(IV) probe (theta(M) = 240 K) is found to be slightly higher than for the Sn(II) one (theta(M) = 217 K).