  In classical thermodynamics the entropy is an extensive quantity, i.e.\ the
sum of the entropies of two subsystems in equilibrium with each other is equal
to the entropy of the full system consisting of the two subsystems. The
extensitivity of entropy has been questioned in the context of a theoretical
foundation for the so-called $\kappa$-distributions, which describe plasma
constituents with power-law velocity distributions. We demonstrate here, by
employing the recently introduced {\it regularized $\kappa$-distributions},
that entropy can be defined as an extensive quantity even for such
power-law-like distributions that truncate exponentially.
