The Interferometric Monitor for Greenhouse Gases (IMG) operated aboard the polar-orbiting Advanced Earth Observing Satellite from October 1996 through June 1997. The IMG measured upwelling infrared radiance at fine spectral resolution. This paper identifies previously undocumented issues with IMG interferograms and describes procedures for correcting the majority of the affected data. In particular, single-sided interferograms should be used to avoid large noise bursts, and phase ambiguities must be resolved in uncalibrated spectra before radiometric calibration. The corrections are essential for studies that require accurately calibrated radiance spectra, including those that track atmospheric changes globally on decadal time scales.