In his (2004), Randolph Clarke assesses an important version of an influential argument against libertarianism about metaphysical freedom. Clarke calls the anti-libertarian argument he evaluates the Contrast Argument. It targets the following claim: there could be an undetermined free act done by S such that S would have freely done something else had S not done the act in question. This modal claim will be endorsed not only by proponents of main brands of libertarianism, but also by action theorists of other stripes – including many compatibilists. Clarke aims to defend the Contrast Argument from a prominent objection by developing a novel case for the premise under attack. I show that Clarke's attempted defense of the Contrast Argument fails, thereby protecting the relevant libertarian and compatibilist positions. In brief, Clarke's argument depends on an ambiguous principle, each available reading of which leaves some or other premise of his argument unjustified.