Tertullian

But perhaps, to avoid this difficulty, you will say that he therefore added just afterwards, "Though an angel from heaven preach any other gospel, let him be accursed," because he was aware that the Creator was going to introduce a gospel! But you thus entangle yourself still more.

His meaning, however, is clear, for he has mentioned himself first (in the anathema): "But though we or an angel from heaven preach any other gospel." It is by way of an example that he has expressed himself.