SAN FRANCISCO — A Southern California court of appeal has broken with 30 years of case law in reversing an alleged pimp’s conviction for trying to make a woman a prostitute, because the woman he was recruiting was already engaged in prostitution.

The Fourth District Court of Appeal ruled that the conviction couldn’t stand because the law governing pandering specifically describes victims as pressured to “become” a prostitute. The ruling, issued Thursday, appears to decriminalize the act of persuading a prostitute to “change her business relationship.”