A right R-module P is $c$-separative provided that $$P{oplus}P{{c}atop{simeq_-}}P{oplus}Q{Longrightarrow}P{simeq_-}Q$$ for any right R-module Q. We get, in this paper, two sufficient conditions under which a right module is $c$-separative. A ring R is a hereditary ring provided that every ideal of R is projective. As an application, we prove that every projective right R-module over a hereditary ring is $c$-separative.