What is the standard for reviewing a trial judge's refusal to give a proposed jury instruction?

Because the standard by which we review a trial judge's refusal to give a proposed jury instruction is somewhat unclear, see United States v. Ayers, 924 F.2d 1468, 1475 (9th Cir.1991), we have applied the stricter de novo standard. See United States v. Doubleday, 804 F.2d 1091, 1093 (9th Cir.1986). The district court commits reversible error by refusing to instruct the jury on the defendant's theory of the case if the theory is legally sound and evidence in the case makes it applicable. Id. at 1095. A defendant is not entitled to a jury instruction where there is no evidence to support it. Id. (quoting United States v. Falsia, 724 F.2d 1339, 1342 (9th Cir.1983)).