opinion: MARYLAND v. GARRISON
  No. 85-759.
  Argued November 5, 1986
  Decided February 24, 1987
  Stevens, J., delivered the opinion of the Court, in which Rehnquist, C. J., and White, Powell, O’Connor, and Scalia, JJ., joined. Black-mun, J., filed a dissenting opinion, in which Brennan and Marshall, JJ., joined, post, p. 89.
  Stephen H. Sachs, Attorney General of Maryland, argued the cause for petitioner. With him on the briefs were Deborah K. Chasanow and Anne E. Singleton, Assistant Attorney General.
  Gerald A. Kroop argued the cause and filed a brief for respondent.
  Briefs of amici curiae urging reversal were filed for the State of California by John K. Van de Kamp, Attorney General, Steve White, Chief Assistant Attorney General, and Ronald E. Niver and Clifford K. Thompson, Jr., Deputy Attorneys General; and for Americans for Effective Law Enforcement, Inc., et al. by Fred E. Inbau, Wayne W. Schmidt, James P. Manak, David Crump, Daniel B. Hales, and Jack E. Yelverton.
  Justice Stevens
  delivered the opinion of the Court.
  Baltimore police officers obtained and executed a warrant to search the person of Lawrence McWebb and “the premises known as 2036 Park Avenue third floor apartment.” When the police applied for the warrant and when they conducted the search pursuant to the warrant, they reasonably believed that there was only one apartment on the premises described in the warrant. In fact, the third floor was divided into two apartments, one occupied by McWebb and one by respondent Garrison. Before the officers executing the warrant became aware that they were in a separate apartment occupied by respondent, they had discovered the contraband that provided the basis for respondent’s conviction for violating Maryland’s Controlled Substances Act. The question presented is whether the seizure of that contraband was prohibited by the Fourth Amendment.
  The trial court denied respondent’s motion to suppress the evidence seized from his apartment, App. 46, and the Maryland Court of Special Appeals affirmed. 58 Md. App. 417, 473 A. 2d 514 (1984). The Court of Appeals of Maryland reversed and remanded with instructions to remand the case for a new trial. 303 Md. 385, 494 A. 2d 193 (1985).
  There is no question that the warrant was valid and was supported by probable cause. Id., at 392, 494 A. 2d, at 196. The trial court found, and the two appellate courts did not dispute, that after making a reasonable investigation, including a verification of information obtained from a reliable informant, an exterior examination of the three-story building at 2036 Park Avenue, and an inquiry of the utility company, the officer who obtained the warrant reasonably concluded that there was only one apartment on the third floor and that it was occupied by McWebb. App. 41; 58 Md. App., at 433, 473 A. 2d, at 522; 303 Md., at 387-390, 494 A. 2d, at 194-195. When six Baltimore police officers executed the warrant, they fortuitously encountered McWebb in front of the building and used his key to gain admittance to the first-floor hallway and to the locked door at the top of the stairs to the third floor. As they entered the vestibule on the third floor, they encountered respondent, who was standing in the hallway area. The police could see into the interior of both Mc-Webb’s apartment to the left and respondent’s to the right, for the doors to both were open. Only after respondent’s apartment had been entered and heroin, cash, and drug paraphernalia had been found did any of the officers realize that the third floor contained two apartments. App. 41-46. As soon as they became aware of that fact, the search was discontinued. Id., at 32, 39. All of the officers reasonably believed that they were searching McWebb’s apartment. No further search of respondent’s apartment was made.
  The matter on which there is a difference of opinion concerns the proper interpretation of the warrant. A literal reading of its plain language, as well as the language used in the application for the warrant, indicates that it was intended to authorize a search of the entire third floor. This is the construction adopted by the intermediate appellate court, see 58 Md. App., at 419, 473 A. 2d, at 515, and it also appears to be the construction adopted by the trial judge. See App. 41. One sentence in the trial judge’s oral opinion, however, lends support to the construction adopted by the Court of Appeals, namely, that the warrant authorized a search of McWebb’s apartment only. Under that interpretation, the Court of Appeals concluded that the warrant did not authorize the search of respondent’s apartment and the police had no justification for making a warrantless entry into his premises.
  The opinion of the Maryland Court of Appeals relies on Article 26 of the Maryland Declaration of Rights and Maryland cases as well as the Fourth Amendment to the Federal Constitution and federal cases. Rather than containing any “plain statement” that the decision rests upon adequate and independent state grounds, see Michigan v. Long, 463 U. S. 1032, 1042 (1983), the opinion indicates that the Maryland constitutional provision is construed in pari materia with the
  Fourth Amendment. We therefore have jurisdiction. Because the result that the Court of Appeals reached did not appear to be required by the Fourth Amendment, we granted certiorari. 475 U. S. 1009 (1986). We reverse.
  In our view, the case presents two separate constitutional issues, one concerning the validity of the warrant and the other concerning the reasonableness of the manner in which it was executed. See Dalia v. United States, 441 U. S. 238, 258 (1979). We shall discuss the questions separately.
  I-H
  The Warrant Clause of the Fourth Amendment categorically prohibits the issuance of any warrant except one “particularly describing the place to be searched and the persons or things to be seized.” The manifest purpose of this particularity requirement was to prevent general searches. By limiting the authorization to search to the specific areas and things for which there is probable cause to search, the requirement ensures that the search will be carefully tailored to its justifications, and will not take on the character of the wide-ranging exploratory searches the Framers intended to prohibit. Thus, the scope of a lawful search is “defined by the object of the search and the places in which there is probable cause to believe that it may be found. Just as probable cause to believe that a stolen lawnmower may be found in a garage will not support a warrant to search an upstairs bedroom, probable cause to believe that undocumented aliens are being transported in a van will not justify a warrantless search of a suitcase.” United States v. Ross, 456 U. S. 798, 824 (1982).
  In this case there is no claim that the “persons or things to be seized” were inadequately described or that there was no probable cause to believe that those things might be found in “the place to be searched” as it was described in the warrant. With the benefit of hindsight, however, we now know that the description of that place was broader than appropriate because it was based on the mistaken belief that there was only one apartment on the third floor of the building at 2036 Park Avenue. The question is whether that factual mistake invalidated a warrant that undoubtedly would have been valid if it had reflected a completely accurate understanding of the building’s floor plan.
  Plainly, if the officers had known, or even if they should have known, that there were two separate dwelling units on the third floor of 2036 Park Avenue, they would have been obligated to exclude respondent’s apartment from the scope of the requested warrant. But we must judge the constitutionality of their conduct in light of the information available to them at the time they acted. Those items of evidence that emerge after the warrant is issued have no bearing on whether or not a warrant was validly issued. Just as the discovery of contraband cannot validate a warrant invalid when issued, so is it equally clear that the discovery of facts demonstrating that a valid warrant was unnecessarily broad does not retroactively invalidate the warrant. The validity of the warrant must be assessed on the basis of the information that the officers disclosed, or had a duty to discover and to disclose, to the issuing Magistrate. On the basis of that information, we agree with the conclusion of all three Maryland courts that the warrant, insofar as it authorized a search that turned out to be ambiguous in scope, was valid when it issued.
  II
  The question whether the execution of the warrant violated respondent’s constitutional right to be secure in his home is somewhat less clear. We have no difficulty concluding that the officers’ entry into the third-floor common area was legal; they carried a warrant for those premises, and they were accompanied by McWebb, who provided the key that they used to open the door giving access to the third-floor common area. If the officers had known, or should have known, that the third floor contained two apartments before they entered the living quarters on the third floor, and thus had been aware of the error in the warrant, they would have been obligated to limit their search to McWebb’s apartment. Moreover, as the officers recognized, they were required to discontinue the search of respondent’s apartment as soon as they discovered that there were two separate units on the third floor and therefore were put on notice of the risk that they might be in a unit erroneously included within the terms of the warrant. The officers’ conduct and the limits of the search were based on the information available as the search proceeded. While the purposes justifying a police search strictly limit the permissible extent of the search, the Court has also recognized the need to allow some latitude for honest mistakes that are made by officers in the dangerous and difficult process of making arrests and executing search warrants.
  In Hill v. California, 401 U. S. 797 (1971), we considered the validity of the arrest of a man named Miller based on the mistaken belief that he was Hill. The police had probable cause to arrest Hill and they in good faith believed that Miller was Hill when they found him in Hill’s apartment. As we explained:
  “The upshot was that the officers in good faith believed Miller was Hill and arrested him. They Were quite wrong as it turned out, and subjective good-faith belief would not in itself justify either the arrest or the subsequent search. But sufficient probability, not certainty, is the touchstone of reasonableness under the Fourth Amendment and on the record before us the officers’ mistake was understandable and the arrest a reasonable response to the situation facing them at the time.” Id., at 803-804.
  While Hill involved an arrest without a warrant, its underlying rationale that an officer’s reasonable misidentification of a person does not invalidate a valid arrest is equally applicable to an officer’s reasonable failure to appreciate that a valid warrant describes too broadly the premises to be searched. Under the reasoning in Hill, the validity of the search of respondent’s apartment pursuant to a warrant authorizing the search of the entire third floor depends on whether the officers’ failure to realize the overbreadth of the warrant was objectively understandable and reasonable. Here it unquestionably was. The objective facts available to the officers at the time suggested no distinction between McWebb’s apartment and the third-floor premises.
  For that reason, the officers properly responded to the command contained in a valid warrant even if the warrant is interpreted as authorizing a search limited to McWebb’s apartment rather than the entire third floor. Prior to the officers’ discovery of the factual mistake, they perceived McWebb’s apartment and the third-floor premises as one and the same; therefore their execution of the warrant reasonably included the entire third floor. Under either interpretation of the warrant, the officers’ conduct was consistent with a reasonable effort to ascertain and identify the place intended to be searched within the meaning of the Fourth Amendment. Cf. Steele v. United States, 267 U. S. 498, 503 (1925).
  The judgment of the Court of Appeals is reversed, and the case is remanded for further proceedings not inconsistent with this opinion.
  It is so ordered.
  App. 9, 41. The warrant was issued and executed on May 21, 1982. It authorized the Baltimore police to search the person of McWebb and “the premises known as 2036 Park Avenue third floor apartment” for “Marihuana, related paraphernalia, minies, books, papers, and photographs pertaining to the illegal distribution of Marihuana . . . .” Id., at 9.
  While the search was in progress, an officer in respondent’s apartment answered the telephone. The caller asked for “Red Cross”; that was the name by which McWebb was known to the confidential informant. Id., at 6. Neither respondent nor McWebb indicated to the police during the search that there were two apartments. Id., at 38, 39-40.
  The warrant states:
  “Affidavit having been made before me by Detective Albert Marcus, Baltimore Police Department, Narcotic Unit, that he has reason to believe that on the person of Lawrence Meril McWebb . . . [and] that on the premises known as 2036 Park Avenue third floor apartment, described as a three story brick dwelling with the numerals 2-0-3-6 affixed to the front of same in the City of Baltimore, there is now being concealed certain property ....
  “You are therefor commanded, with the necessary and proper assistants, to search forthwith the person/premises hereinabove described for the property specified, executing this warrant and making the search . . . .” Id., at 9.
  Immediately before ruling on the suppression motions made by McWebb and Garrison, the court observed that a search of two or more apartments in the same building must be supported by probable cause for searching each apartment. The court added, “[t]here is an exception to this general rule where the multiple unit character of the premises is not externally apparent and is not known to the officer applying for or executing the warrant.” Id., at 45. The trial court then ruled, “It is clear that the warrant specified the premises to be searched as the third floor apartment of the Defendant McWebb . . . .” Id., at 46. This statement only makes sense as a rejection of Garrison’s claim that “the warrant was a general warrant as it did not specify which apartment was to be searched on the third floor,” id., at 40, and as a recognition that the search was not invalid for lack of specificity in the warrant as to the premises to be searched. We interpret the trial court’s statement as a ruling that the search of a subunit of the building — which he referred to as “the third floor apartment of the Defendant McWebb” — was authorized by the warrant. The court then found on the precise facts of this ease that the search of Garrison’s apartment was valid because “the officers did not know that there was more than one apartment on the third floor and nothing alerted them of such a fact until after the search had been made and the items were [seized].” Id., at 46. The contrary construction adopted by the Court of Appeals fails to take into account the plain language of the warrant, which authorized a search of the person of McWebb and of the premises of 2036 Park Avenue, third floor. Id., at 9.
  As the Court of Appeals explained:
  “It is undisputed that the police were authorized to search only one apartment, MeWebb’s; the warrant did not authorize the search of Garrison’s apartment. There is no question as to the validity of the search warrant itself. No argument was made in this Court that any of the exceptions to the warrant requirement applied here. It is clear, therefore, that the police had no authority to cross the threshold of Garrison’s apartment and seize evidence.
  “Police had a warrant to search MeWebb’s apartment. They had no warrant to search Garrison’s. They had no justification for entering his premises, regardless of appearances.” 303 Md. 386, 392r394, 494 A. 2d, 193, 196-197 (1985).
  Article 26 of the Maryland Declaration of Rights provides:
  “That all warrants, without oath or affirmation, to search suspected places, or to seize any person or property, are grevious [grievous] and oppressive; and all general warrants to search suspected places, or to apprehend suspected persons, without naming or describing the place, or the person in special, are illegal, and ought not to be granted.”
  303 Md., at 391, 494 A. 2d, at 196. This statement indicates that the “state court decision fairly appears to rest primarily on federal law, or to be interwoven with the federal law . . . .” Michigan v. Long, 463 U. S., at 1040.
  See Andresen v. Maryland, 427 U. S. 463, 480 (1976); Stanley v. Georgia, 394 U. S. 557, 569-572 (1969) (Stewart, J., concurring in result); Stanford v. Texas, 379 U. S. 476, 481-482, 485 (1965); Go-Bart Importing Co. v. United States, 282 U. S. 344, 357 (1931); Marron v. United States, 275 U. S. 192, 195-196 (1927).
  Cf. United States v. Jacobsen, 466 U. S. 109, 115 (1984) (warrantless test of white powder; “[t]he reasonableness of an official invasion of the citizen’s privacy must be appraised on the basis of the facts as they existed at the time that invasion occurred”).
  Arguments can certainly be made that the police in this case should have been able to ascertain that there was more than one apartment on the third floor of this building. It contained seven separate dwelling units and it was surely possible that two of them might be on the third floor. But the record also establishes that Officer Marcus made specific inquiries to determine the identity of the occupants of the third-floor premises. The officer went to 2036 Park Avenue and found that it matched the description given by the informant: a three-story brick dwelling with the numerals 2-0-3-6 affixed to the front of the premises. App. 7. The officer “made a cheek with the Baltimore Gas and Electric Company and discovered that the premises of 2036 Park Ave. third floor was in the name of Lawrence McWebb.” Ibid. Officer Marcus testified at the suppression hearing that he inquired of the Baltimore Gas and Electric Company in whose name the third floor apartment was listed: “I asked if there is a front or rear or middle room. They told me, one third floor was only listed to Lawrence McWebb.” Id., at 36-38. The officer also discovered from a check with the Baltimore Police Department that the police records of Lawrence McWebb matched the address and physical description given by the informant. Id., at 7. The Maryland courts that are presumptively familiar with local conditions were unanimous in concluding that the officer reasonably believed McWebb was the only tenant on that floor. Because the evidence supports their conclusion, we accept that conclusion for the purpose of our decision.
  “Because many situations which confront officers in the course of executing their duties are more or less ambiguous, room must be allowed for some mistakes on their part. But the mistakes must be those of reasonable men, acting on facts leading sensibly to their conclusions of probability.” Brinegar v. United States, 338 U. S. 160, 176 (1949).
  Nothing McWebb did or said after he was detained outside 2036 Park Avenue would have suggested to the police that there were two apartments on the third floor. McWebb provided the key that opened the doors on the first floor and on the third floor. The police could reasonably have believed that McWebb was admitting them to an undivided apartment on the third floor. When the officers entered the foyer on the third floor, neither McWebb nor Garrison informed them that they lived in separate apartments. App. 39-40, 42.
  We expressly distinguish the facts of this case from a situation in which the police know there are two apartments on a certain floor of a building, and have probable cause to believe that drugs are being sold out of that floor, but do not know in which of the two apartments the illegal transactions are taking place. A search pursuant to a warrant authorizing a search of the entire floor under those circumstances would present quite different issues from the ones before us in this case.
  Respondent argued that the execution of the warrant violated the Fourth Amendment at the moment when the officers “walked in through that threshold of that house . . . .” Tr. ofOralArg. 35. At another point respondent argued that the search was illegal at the point when the police went through Garrison’s apartment without probable cause for his apartment. Id., at 43. For the purpose of addressing respondent’s argument, the exact point at which he asserts the search became illegal is not essential. Whether the illegal threshold is viewed as the beginning of the entire premises or as the beginning of those premises that, upon closer examination, turn out to be excluded from the intended scope of the warrant, we cannot accept respondent’s argument. It would brand as illegal the execution of any warrant in which, due to a mistake in fact, the premises intended to be searched vary from their description in the warrant. Yet in this case, in which the mistake in fact does not invalidate the warrant precisely because the police do not know of the mistake in fact when they apply for, receive, and prepare to execute the warrant, the police cannot reasonably know prior to their search that the warrant rests on a mistake in fact. It is only after the police begin to execute the warrant and set foot upon the described premises that they will discover the factual mistake and must reasonably limit their search accordingly.
  Respondent proposes that the police conduct a preliminary survey of the premises whenever they search a building in which there are multiple dwelling units, in order to determine the extent of the premises to be searched. Id., at 42. We find no persuasive reason to impose such a burden over and above the bedrock requirement that, with the exceptions we have traced in our cases, the police may conduct searches only pursuant to a reasonably detailed warrant.
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