Abstract: A method of retrofitting a tooth unit to a trailing edge of a wind turbine rotor blade. A portion of the trailing edge of the rotor blade is cut out and removed. That can be affected when the rotor blade is still disposed on a hub of the wind power installation (that is to say in the mounted state). A tooth retrofitting unit is glued or adhesively fixed on the trailing edge of the wind turbine rotor blade in the cut-out and removed portion. The tooth retrofitting unit has a V-shaped profile and at its first side has two fixing arms and at an opposite side a plurality of teeth. The two fixing arms are adhesively secured to the trailing edge of the rotor blade to mount the tooth retrofitting unit.