Larry D. Semenza was convicted of two counts of allowing unauthorized livestock to trespass on National Forest Land in violation of 36 C.F.R. § 261.7 (a). 644 F.Supp. 780 . That regulation prohibits “[p]lacing or allowing unauthorized livestock to enter or be in the National Forest System or other lands under Forest Service control.” The regulation was promulgated pursuant to 16 U.S.C. § 551 (1982).

Semenza’s cattle had been sighted repeatedly on National Forest Lands. Forest Service employees had made positive identifications on each of the dates charged in the indictment. Semenza did not have a permit to graze his cattle. Semenza had the sole legal responsibility for restraining his livestock from entering and remaining on Forest Service lands. Semenza contends that he cannot be convicted of violating the regulation unless there is some evidence of a purposeful action or inaction by him resulting in the livestock’s unauthorized presence. Alternatively, he urges that he is entitled to a new trial on the basis of new evidence. We reverse.

The first issue we must resolve is whether § 261.7(a) requires a criminal intent. The interpretation of a regulation raises a question of law which we review de novo. United States v. Varbel, 780 F.2d 758, 761 (9th Cir.1986). It is the Government’s position that § 261.7(a) creates a strict liability crime. In support of this position, we are urged to adopt the reasoning of the Eighth Circuit, the only court that has interpreted § 261.7(a). See United States v. Larson, 746 F.2d 455 (8th Cir.1984). The Larson court noted that “[i]ntent ... is not an essential element of § 261.7.” Larson, 746 F.2d at 456 . We reject the finding of the Eighth Circuit.

Absent a clear indication of legislative intent, courts should be reluctant to dispense with a mens rea requirement. Morissette v. United States, 342 U.S. 246, 263 , 72 S.Ct. 240, 249 , 96 L.Ed. 288 (1952). The Department of Agriculture regulation did not make unauthorized entrance or presence on Forest Service land a per se violation. The operative language of § 261.7(a) prohibits “allowing unauthorized livestock to enter or be” on Forest Service land, (emphasis added). Criminal liability may only be imposed against the defendant if the defendant has allowed the livestock’s entrance or presence.

The word allow “has no rigid or precise meaning,” but, in the context in which it is used in the regulation, may mean “to acquiesce in; to suffer; to tolerate.” Black’s Law Dictionary 70 (5th ed. 1979). We think it proper to give it the same meaning as permit or suffer. We construed those two words in United States v. Launder, 743 F.2d 686 (9th Cir.1984). In that case a hiker who became lost and set a signal fire to attract rescuers started a forest fire. He was convicted of violating 18 U.S.C. § 1856 , which makes it a crime when a person “permits or suffers [a] fire to burn or spread beyond his control” in federal forests. We reversed, holding that these words were “not the language of strict liability. The legal terms ‘permitting’ and ‘suffering’ clearly require a willful act or a willful failure to act in the face of a clear opportunity to do so.” Id. at 689 .

We find no reason why the analysis of the regulation at issue in this case should differ from that used in Launder . *225 In addition to proof that the livestock were on Forest Service land, that they were unauthorized, and that the defendant had responsibility to control the livestock in question, the language of § 261.7(a) requires an additional element. The Government must prove that the defendant willfully acted to allow his cattle to enter the National Forest, or willfully failed to prevent their entering when he had a clear opportunity to do so.

There is evidence in the record that could support a trier of fact’s finding that Se-menza willfully failed to keep his cattle off Forest Service lands when he had a clear opportunity to do so. There is also evidence that could support a contrary finding. As an appellate court, we are not free to resolve this issue. See Dunn v. United States, 442 U.S. 100, 107 , 99 S.Ct. 2190, 2194 , 60 L.Ed.2d 743 (1979) (“appellate courts are not free to revise the basis on which a defendant is convicted simply because the same result would likely obtain on retrial”); United States v. Castillo-Felix, 539 F.2d 9, 13 (9th Cir.1976) (appellate court not free to affirm conviction “reached on the basis of a wrong reason”; defense attorney might have taken different approach if case had been properly framed). Semenza is accordingly entitled to a new trial governed by a proper construction of § 261.7(a). 1

REVERSED AND REMANDED.

. In light of our disposition, we need not address Semenza’s claim that the district court erred in denying his motion for new trial on the ground of newly discovered evidence.