This Article analyzes Heien v. North Carolina, in which the Supreme Court considered whether an officer's stop of a motorist could be considered a reasonable seizure under the Fourth Amendment even though it was based on a police officer's mistake of law regarding the state's traffic code. The Heien Court ruled that an officer's mistake of law could be objectively reasonable and therefore contribute to the reasonable suspicion needed to support a traffic stop. This work examines the concerns created by Heien's ruling. This Article asserts that, in allowing an officer to seize a person on the basis of that officer's mistaken belief that the individual violated the law, Heien could encourage stops and arrests based on unclear laws that could cause Fourteenth and Fourth Amendment problems. Further, Heien's conclusion that an officer's mistake of law can be reasonable is inconsistent with the Court's Fourth Amendment balancing analysis for assessing reasonableness. Heien's allowance of police mistakes of law could impair police professionalism and undermine public confidence in law enforcement. Finally, Heien's acceptance of officers' mistakes of law could cause serious negative consequences for motorists beyond the initial seizure.