During the Mt. Kelud Feb 2014 eruption the ash cloud was detectable on 13–14 Feb in the infrared with the reverse absorption technique by, for example, the Advanced Very High Resolution Radiometer (AVHRR/3). The Infrared Atmospheric Sounding Interferometer (IASI) observed the ash cloud also on 15 Feb when AVHRR did not detect any ash signal. The differences between ash detection with AVHRR/3 and IASI are discussed and the reasons for the differences supported with radiative transfer modelling. The effect of conccurent ice clouds on the ash detection and the ash signal in the IASI measurements is demonstrated. Specifically, a radiative transfer model is used to simulate IASI spectra with ash only, with ice cloud only and with both ash and ice clouds. It is shown that modelled IASI spectra with ash and ice clouds better reproduce the measured IASI spectra than ash only or ice only modelled spectra. The ash and ice modelled spectra that best reproduce the IASI spectra contain about a factor of 14 less ash than the ash only spectra that come closest to reproducing the measured spectra.