Arminius taught that Calvinist predestination and unconditional election made God the author of evil.
But making God the author of evil is not something we have to infer into Calvin’s doctrine. He explicitly stated it:
'I have already shown clearly enough that God is the author of all those things which, according to these objectors, happen only by his inactive permission. He testifies that he creates light and darkness, forms good and evil (Is 45:7); that no evil happens which he hath not done (Amos 3:6).' - Institutes , Bk. I. 18:3
Incredibly Calvin claims that sinners do not commit acts of depravity in spite of God’s commands, but because of the command of God.