A non-Arrhenius variation of conductivity below T-g is shown to exist in the fast ion conducting glass 0.5Ag(2)S-0.5GeS(2). Such a behaviour appears to be a characteristic of fast ion conductors, either crystallized (CFIC) or glassy (GFIC). The empirical Vogel-Fulcher-Tammann law is used to account for conductivity variations in all these materials. This behaviour is probably the manifestation of the configurational entropy associated with the cation disordering which is a common characteristic to both GFIC and CFIC.