There is a need for a consistent time-series of NDVI data for vegetation monitoring in Africa. In this work, we explore the compatibility of the FAOARTEMIS and NASA Pathfinder AVHRR Land NDVI archives. Values from the two archives were found to be significantly and systematically different even for the recently corrected form of the Pathfinder archive. Differences are attributable to the different processing chains used on essentially the same raw data. The two archives should not be mixed together for time-series analysis of NDVI, without correction. Although differences varied for periods of the record covered by different satellites, these were practically small and we present a single linear relation to correct one series values to the same basis as the other.