Echo-planar imaging is subject to Nyquist ghosting due to its use of fast gradient switching. To correct for this artifact, several methods have been proposed that involve a pair of calibration imaging frames acquired with opposite readout polarities. We show that a small, relative shift in the phase-encoding direction often exists between these calibration frames that may lead to compromised image quality. A simple method is proposed to account for the shift and it is shown to be effective at correcting residual Nyquist ghost in the dual-polarity GRAPPA approach. This is demonstrated in in vivo and phantom data from 3T and 7T.