We investigate the partially asymmetric exclusion process (PASEP) with open boundaries when the reverse hopping rate of particles q = −1, using a representation of the PASEP algebra related to the al-Salam Chihara polynomials. When q = −1 the representation is two-dimensional, which allows for straightforward calculation of the normalization, current and density. We note that these quantities behave in an a priori reasonable manner in spite of the apparently unphysical value of q as the input, α, and output, β, rates are varied over the physical range of 0 to 1.As is well known, another two dimensional representation exists when 0 < q < 1 and abq = 1, where a = (1 − q)/β − 1 and b = (1 − q)/β − 1, and we compare the behaviour at q = −1 with this. An extension to generalized boundary conditions where particles may enter and exit at both ends is briefly outlined. We also note that a different representation related to the q-harmonic oscillator does not admit a straightforward truncation when q = −1 and discuss why this is the case from the perspective of a lattice path interpretation of the PASEP normalization.