A wind turbine blade assembly comprising a wind turbine blade having a tip end and a root end, and a leading edge and a trailing edge with a chord length extending therebetween is described. The wind turbine blade assembly further comprises an aeroshell extender piece comprising a body for attachment to a trailing edge side of a profile of a wind turbine blade, the body having a first end for attachment to the trailing edge side of the profile, and a second trailing edge end to form an extended airfoil trailing edge profile for a portion of the profile of the wind turbine blade. The aeroshell extender piece is attached to the wind turbine blade at least partly using at least one profile wedge, said at least one profile wedge being shaped to compensate for the geometry of the wind turbine blade.