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This paper demonstrates that the equilibrium determined by the commitment of a Central Bank to a non-stationary (“super-inertial”) interest rate rule (where the sum of the parameters of interest rate lags exceeds one and does not depend on the persistence of shocks) does not correspond to the unique bounded solution and the stable equilibrium of Ramsey optimal policy for the new-Keynesian model. It always destabilizes inflation because of the rounding and measurement errors of the parameters of the monetary policy transmission mechanism. By contrast, the commitment of a Central Bank to a stationary interest rate rule (where the sum of the parameters of interest rate lags is strictly below one and depends on the persistence of shocks) corresponds to the unique bounded solution and the stable equilibrium of Ramsey optimal policy. JEL classification numbers. C61, C62, E43, E44, E47, E52, E58