Tertullian

For nobody had induced them to apostatize from the Creator, that they should seem to "be removed to another gospel," simply when they return again to the Creator. When he adds, too, the words, "which is not another," he confirms the fact that the gospel which he maintains is the Creator's.

So that there are two gospels for two gods; and the apostle made a great mistake when he said that "there is not another" gospel, since there is (on the hypothesis) another; and so he might have made a better defence of his gospel, by rather demonstrating this, than by insisting on its being but one.