Further refinement has been carried out on the neutron diffraction data for potassium bifluoride. Best agreement was obtained for a physically impossible model which must be rejected on other grounds. Following Ibers, the hydrogen atom is assumed to be centrally located. Combination of spectroscopic and diffraction data from sodium, potassium, and ammonium bifluorides allows a detailed analysis of the thermal motions to be made. The average F ···F distance, after correction, is found to be 2.292 ± 0.004 Å.