Is a district court's denial of a proposed jury instruction reviewed de novo or for an abuse of discretion?

This circuit has not resolved the issue of whether a district court's denial of a proposed jury instruction is reviewed de novo or for an abuse of discretion. United States v. Streit, 962 F.2d 894, 897 (9th Cir.1992). However, it is not necessary to resolve this issue on the present appeal because the result would be the same under either standard. If a theory of defense is legally sound and supported by the evidence, the district court's failure to instruct the jury on the theory is reversible error. United States v. Lemon, 824 F.2d at 764.