The present invention relates to a method of performing at least one post-moulding operation on a blade segment (70) of a wind turbine blade. The method comprises the providing a holding device (88) for supporting the blade segment (70) at its spar structure (62), the holding device (88) comprising a coupling member (90) for engaging the spar structure (62). The blade segment (70) is held with the holding device (88) such that the spar structure (62) of the blade segment (70) is engaged by the coupling member (90), and performing at least one post-moulding operation on the shell structure (82) of the blade segment (70).