What is the test for giving a jury instruction on an affirmative defense?

A jury instruction on an affirmative defense is appropriate "only if it appears that the defendant is relying on such a defense, or if there is substantial evidence supportive of such a defense and the defense is not inconsistent with the defendant's theory of the case." (People v. Sedeno (1974) 10 Cal.3d 703, 716, italics added, overruled on other grounds by People v. Breverman (1998) 19 Cal.4th 142, 157, 172-179.)