A 26-year-old Caucasian female in her second pregnancy grouped as A, D+ R1R1 K− with anti-K (titre: 256) at booking. Her partner was typed as K1 positive. Baby was born with Hb 23.1 g/dl. Cord samples were referred to our laboratory for investigation and were found to be DAT 5+, IgG and anti-K was eluted from the red cells. Cord samples typed as A, R1r K− by DiaMed DiaClon Rh subgroups & K card. We report a case of false negative K1 phenotyping due to blocking with maternal anti-K.