A simple criterion is derived for determining the sign of the pseudomomentum of neutral modes in shallow water systems. The sign of the pseudomomentum is determined by the gradient of the dispersion curve on a wavenumber vs. phase-speed plane: a mode has pseudomomentum with the opposite sign to that of the gradient of the dispersion curve. In most cases, the sign of the pseudomomentum is also determined only from the value of its phase speed: the pseudomomentum of a mode is positive if its phase speed is faster than the velocity of the basic flow at any point and vice versa, but with a few exceptions.