939.43 Mistake.
(1) An honest error, whether of fact or of law other than criminal law, is a defense if it negatives the existence of a state of mind essential to the crime.
(2) A mistake as to the age of a minor or as to the existence or constitutionality of the section under which the actor is prosecuted or the scope or meaning of the terms used in that section is not a defense.
The prosecution of an individual who relied on a governmental official's statutorily required legal opinion would impose an unconscionable rigidity in the law. State v. Davis, 63 Wis. 2d 75, 216 N.W.2d 31 (1974).
Mistake is not a defense to criminal negligence. A defendant's subjective state of mind is not relevant to determining criminal negligence. State v. Lindvig, 205 Wis. 2d 100, 555 N.W.2d 197 (Ct. App. 1996), 96-0235.