We present an experimental study of the temperature dependence of the metal-molecule stretch vibrational mode of CO chemisorbed on a Pt(111) surface using infrared spectroscopy. The previously reported doublet structure in the vicinity of the Pt-CO stretch for bridge bonded (CO)-C-12-O-16, which we assigned to a Fermi resonance, exhibits a strong temperature dependence. The doublet vanishes at 50 K, reducing to one single peak with twice the intensity. This supports our previous interpretation and we are in this paper able to discuss this Fermi resonance in more detail. In addition, we have investigated how the Fourier transform infrared technique may influence the observed peak widths.