  We investigate the hypothesis that the higher-derivative corrections always
make extremal non-supersymmetric black holes lighter than the classical bound
and self-repulsive. This hypothesis was recently formulated in the context of
the so-called swampland program. One of our examples involves an extremal
heterotic black hole in four dimensions. We also calculate the effect of
general four-derivative terms in Maxwell-Einstein theories in D dimensions. The
results are consistent with the conjecture.
