Amplitude of a wave

According to Physics Matters GEO 'O' Level Physics (4th edition) by C. Chew, S.F. Chow and B.T. Ho:

The amplitude of a wave is the maximum displacement of a point from its rest position.

Since displacement can take negative values, can amplitude take negative values too?

But according to Fundamentals of Physics (10th edition) by D. Halliday, R. Resnick and J. Jewett,

The amplitude of a wave is the magnitude of the maximum displacement of the elements from their equilibrium positions as the wave passes through them.

So I guess Physics Matters GEO 'O' Level Physics might need to change their definition of amplitude so that the HA students would not think that amplitude can take negative values.