It is shown that electron diffraction patterns taken from small areas (typically 4-20 nm) of GaN cross-section TEM specimens allow unequivocal determination of the local polarity. As experimental data we used a set of diffraction patterns from an area with the same polarity but with an increasing thickness due to the wedge-shaped morphology of the TEM specimen. The polarity is determined using a least-squares refinement procedure in which the local misorientation and specimen thickness is refined for the two possible polarities. The refinements show that one polarity has much better agreement between calculated and experimental intensities of the reflections for all diffraction patterns of the set, allowing straightforward identification of polarity.