During our recent characterization of pfhrp2 in parasite isolates collected from several countries as part of the World Health Organisation (WHO) – Foundation for Innovative New Diagnostics (FIND) malaria RDT evaluation program [32], we identified a number of P. falciparum samples collected in Iquitos, Peru, that were positive by microscopy but tested negative with HRP2-detecting RDTs. The gene discussed is HDGFL2; the disease is malaria.