In the case of Maryland v. Garrison, the U.S. Supreme Court ruled in 1986 that a search warrant executed on an apartment mistakenly believed to be part of another apartment was valid under the Fourth Amendment, which protects against unreasonable searches and seizures. The police had obtained a warrant for a third-floor apartment but did not know there were two separate apartments on that floor; they thought it was all one unit. When they entered what turned out to be Garrison's separate residence within this space, they found illegal drugs and charged him accordingly. Garrison argued his conviction should be overturned because the police didn't have a proper warrant for his specific dwelling place when they discovered these drugs. The court held (in a 6-3 decision) that given their reasonable belief at the time of entry - based on information from building management - about how many units were present, their actions fell within an honest mistake or "reasonable error" margin permitted by law enforcement during such operations.

In the dissenting opinion for Maryland v. Garrison, Justice Brennan, joined by Justice Marshall, argued that the majority's decision eroded Fourth Amendment protections against unreasonable searches and seizures. They contended that police officers should be held to a higher standard of "reasonable belief" when executing search warrants. In this case, they believed it was not reasonable for officers to assume there was only one apartment on the third floor when in fact there were two separate units. The dissenters felt that this mistake invalidated any evidence found in Garrison's apartment as it was obtained through an unlawful search under incorrect assumptions about the premises' layout. They stressed that such mistakes could lead to serious invasions of privacy if left unchecked and urged for greater scrutiny over law enforcement actions during searches.