A guaranteed protection against vague laws is know as due process.
Vague laws are hazy, uncertain or imprecise. A criminal statue is void for vagueness if it is so vague that it fails to give a person a fair notice of which conduct is prohibited or required ( it is too vague for an average citizen to understand).
Vague laws deprive citizens of their rights without fair process. The void for vagueness doctrine is a constitutional rule ( 5th and the 14th Amendments).
Due process is the legal requirement that the state must respect all legal rights that are owned to a person. It protects the individual by guaranteeing the due process of law to every citizen. In case of vague laws, the due process can often not be enhanced because the laws are not enough specified or understood, hence not applicable.