Recently, H. Liu et al. [H. Liu, M. Liang, and H. Sun, A secure and efficient certificateless aggregate signature scheme, IEICE Transactions on Fundamentals of Electronics Communications and Computer Sciences, vol.E97-A, no.4, pp.991-915, 2014] proposed a new certificateless aggregate signature (CLAS) scheme and demonstrated that it was provably secure in the random oracle model. However, in this letter, we show that their scheme cannot provide unforgeability, i.e., an adversary having neither the user's secret value nor his/her partial private key can forge a legal signature of any message.