The structure of Mg(ClO2)2.6H2O was described and refined [Okuda, Ishihara, Yamanaka, Ohba & Saito (1990). Acta Cryst. C46, 1755-1759] in the space group P4(2)mc [tetragonal, a = 7.471 (8), c = 9.980 (2) angstrom]; it is better described in P4(2)/nmc (R = 0.024, versus 0.041 previously). Revised coordinates and bond lengths are given.