Segregation of solutes on grain boundaries is usually quantified by the peak value of the concentration profile measured across the grain boundary. This procedure is inadequate both from the theoretical and from the practical point of view. Instead, we put forward the concept of interfacial excess of solute, as having a thermodynamic background and being of operative efficiency. Our analyses reveal carbon and boron co-segregation at a martensite lath boundary of a Dual Phase steel. (C) 2016 Elsevier Ltd. All rights reserved.