A composite structural element comprising a substantially planar main section defining a coordinate system with a first axis extending along a longitudinal axis of the structural element and a second axis extending perpendicular to the longitudinal axis within the planar main section. The structural element contains a basic lay-up of single plies, each comprising a fiber-reinforced composite material with a substantially unidirectional fiber orientation. The lay-up comprises N plies arranged from top to bottom in the following form: [[α, β]M; [γ]K; [β, α]M], wherein α, β and γ represent one ply having an angle enclosed between the first axis and the unidirectional fiber orientation of the one ply, respectively, [x]y means y plies each having angle x; [x, y]z means z pairs of plies, K and M are both positive integers equal to or greater than 1: N=4·M+K.