In Singapore conflict of laws, the tainting doctrine applies where a contractual claim governed by Singapore law is not itself unenforceable for illegality or public policy, but is sufficiently connected to a transaction which is so unenforceable. However, the mechanism of this doctrine—as articulated in the English Court of Appeal decision of Euro-Diam Ltd v Bathurst Ltd—is today uncertain due to, inter alia, its use of domestic illegality principles which no longer apply. This paper suggests two areas of clarification. First, it explores whether the doctrine should be seen an application of the proper law of the contract or the law of the forum. Second, it introduces a possible approach as informed by the test in tainting by domestic illegality, which may be applied where the contract sought to be enforced is governed by Singapore law.