An aggregate signature (AS) scheme combines multiple signatures which is generated by many different users into a single one. This feature is very beneficial for diminishing storage cost, bandwidth and verification cost. Many previous attempts have been made for designing AS schemes, while the former security models have not clearly addressed coalition attacks, and most of the existing AS schemes cannot resist these kinds of attacks. In this study, the authors provide a modified security model of certificateless AS (CLAS) schemes and then give a new CLAS scheme. The security of their present scheme can be rigorously proved based on the computational Diffie–Hellman assumption in the random oracle model. Furthermore, their scheme can resist such coalition attacks, i.e. an AS in their scheme is valid iff all single signatures used to generate the AS are valid.