What is fair warning given to a defendant in a civil case?

While fair warning is the most important indicator a law is not ex post facto, it is not conclusive. One can imagine a statute which would be unconstitutional even though it gave the defendant advance notice how his conduct would be punished. A legislature could not, for example, retroactively make a term mandatory when it was only the maximum permissible term at the time the defendant committed the offense, even though the defendant was on notice of the punishment the state would seek to impose on him if he was found guilty of the offense. (Lindsey v. Washington (1937) 301 U.S. 397, 401.) Such a law would violate the proscription against "arbitrary imprisonment" because it would not deter commission of the offense being punished-that offense already having been committed-it would serve no purpose other than to increase the punishment for the offense.