The relation between the spin period and the orbital period in high-mass X-ray binaries is investigated. Be/X-ray binaries and SG/X-ray binaries occupy different areas in Corbet’s diagram. The two SG/X-ray binaries, IGR J18483-0311 and OAO 1657-415, however, appear to occupy a transition region between Be/X-ray binaries and wind-fed SG/X-ray binaries. This can be understood by noting that the neutron stars in the two SG/X-ray binaries have not reached their equilibrium spin periods when the donors evolved off the main sequence. Here, we provide an alternative scenario to explain their location in Corbet’s diagram: the SG/X-ray binaries are the descendants of Be/X-ray binaries, i.e. the supergiants in these systems were formed from O-type emission line stars instead of normal main-sequence stars. Furthermore, we suggest that there are two types of SG/X-ray binaries: one is directly evolved from a normal OB-type main sequence and neutron star system without an X-ray history, and the other evolved from a Be/X-ray binary with an X-ray history.