Under U.S. criminal law, the general rule is that ignorance of the law or a mistake of law is not a valid defense to criminal prosecution (see also Ignorantia juris non excusat). However, there are exceptions to that rule. Some U.S. criminal statutes provide for what are known as "specific intent" crimes, where ignorance of the law may be a valid defense. The federal criminal tax statutes are examples of statutes for specific intent crimes, where actual ignorance of the law is a valid defense.