The National Environmental Satellite, Data, and Information Service (NESDIS) of the National Oceanic and Atmospheric Administration (NOAA) recently implemented enhancements to its operational calibration processing to mitigate the effects of two performance anomalies affecting the Imagers and Sounders aboard the current Geostationary Operational Environmental Satellites (GOES). This paper describes the anomalies, our algorithm enhancements to mitigate their effects, and results. In the first anomaly, the values of the computed calibration slopes in the infrared channels of the Imagers exhibit erroneous spikes during the six hours surrounding satellite midnight, causing observations of scene temperatures to be too low. We believe the spikes are the result of radiation from the solar-heated scan-cavity that reaches the detectors during the Imagers' calibration cycles. In November 2003, NOAA/NESDIS implemented a statistical algorithm that provides more realistic slopes around midnight. The second anomaly is "banding" in frames of observations by the Sounders' infrared channels. This also occurs during the six hours centered on satellite midnight. We believe the source of this anomaly is rapid changes in the temperatures of Sounder fore-optics components. They cause large and rapid changes in calibration offsets, which are not accounted for properly by the Sounder calibration updates, which only occur once every two minutes. In October 2004, NOAA/NESDIS implemented a remedial algorithm that removes the banding by interpolating the offsets to 1.1s intervals.