Analytical estimates of resistivity due to electrostatic current-driven ion-acoustic waves are compared with Vlasov simulation results. Particular attention is given to the case of similar ion and electron temperatures that is appropriate to the magnetopause and low-latitude boundary layer (LLBL). It is shown that Vlasov simulation runs of growing ion-acoustic waves with Te = 2Ti give values of resistivity which are at least three orders of magnitude higher than an existing analytical estimate <Labelle and Treumann, Sp. Sci. Rev., 47, 1988> and exhibit a different dependence on the wave energy density. A particle-in-cell code was also run with the same temperature ratio and gave similar resistivity values that back up the Vlasov simulation results. The discrepancy between simulation and analytical estimate arises because the derivation of the analytical estimate assumes that the quasilinear effects of the instability are weak. The simulation results show that this is not the case, since plateau formation is clearly seen in the electron distribution function. These simulation results show that the ion-acoustic instability may be more important in the magnetopause and LLBL than previously thought.