Several methods have been devised to measure the weak phase γ using decays of the type B ± → DK ± , where it is assumed that there is no mixing in the D 0 − D 0 system. However, when using these methods to uncover new physics, one must entertain the real possibility that the measurements are affected by new physics effects in the D 0 − D 0 system. We show that even values of xD and/or yD around 10 −2 can have a significant impact in the measurement of sin 2 γ. We discuss the errors incurred in neglecting this effect, how the effect can be checked, and how to include it in the analysis.11.30. Er, 13.25.Ft, 13.25.Hw,