A detachable reinforcement tool (1) for providing temporary reinforcement of a rear frame structure (6) for a nacelle of a wind turbine is disclosed. The rear frame structure (6) comprises a plurality of truss members (4) and a plurality of joints (5), each joint (5) interconnecting ends of at least two truss members (4). The reinforcement tool (1) comprises a reinforcement part (2), and attaching means (3) for detachably attaching the reinforcement part (2) to two different parts (4, 5) of the rear frame structure (6). The reinforcement tool (1) is arranged to provide a load transferring connection between two parts (4, 5) of the rear frame structure (6) when the reinforcement part (2) is attached to the two parts (4, 5) of the rear frame structure (6) by means of the attaching means (3). The rear frame structure (6) is capable of handling extreme loads without being designed to handle such loads permanently. Manufacturing costs and weight of the rear frame structure (6) are reduced.