A counterweight module, a locking element, a counterweight and a method for assembling a counterweight are disclosed. The counterweight module includes a first part and a second part, between which a straight joint is arranged at right angle in relation to the longitudinal direction of the counterweight module. The counterweight locking element can be used to secure the counterweight modules into a counterweight frame. In the method, the counterweight is filled with balancing modules starting from the bottom of the frame.