A method of making a longitudinal reinforcing structure for a wind turbine blade. The method comprises a) providing an elongate master strip (62) of reinforcing material having substantially flat first and second surfaces, the distance between the first and second surfaces defining the thickness of the master strip; and b) dividing the master strip transversely to form a first strip and a shorter master strip, the respective strips being arranged end to end such that a trailing end of the first strip is located adjacent a new leading end of the master strip. The step of dividing the master strip comprises removing material from a dividing region extending through the entire thickness of the master strip, wherein the dividing region is shaped such that a chamfer (19c) at the trailing end (19b) of the first strip is created and a chamfer (63a) at the new leading end (63) of the master strip is created when the master strip is divided.