Schmuck v. United States, 489 U.S. 705 (1989), is a United States Supreme Court decision on criminal law and procedure. By a 5–4 margin it upheld the mail fraud conviction of an Illinois man and resolved a conflict among the appellate circuits over which test to use to determine if a defendant was entitled to a jury instruction allowing conviction on a lesser included charge. Justice Harry Blackmun wrote for the majority; Antonin Scalia for the dissent.