The Reformers on Original Sin
The Reformers further taught that from its very first motion this concupiscence was also sin: it does not first become sin when the will has consented to it, but it is sin in itself, not only as formed, therefore, but already as unformed. Calvin again states that on this point he disagrees with Augustine, who describes concupiscence, after its guilt has been removed from it in baptism, by the word “weakness.” “We, on the other hand, deem it sin.” Finally, this corruption of human nature is so total that humans are by nature incapable of any spiritual good, inclined to all evil, and on account of it alone deserving of eternal punishment.
Reformed Dogmatics: Sin and Salvation in Christ
p. 98
Herman Bavinck. Reformed Dogmatics Volume 3: Sin and Salvation in Christ. Grand Rapids, MI: Baker Books, 2006.