According to CNN, Google is making changes to its advertising policies to prevent “unlawful discrimination” around housing, employment, and credit.

The company will prohibit ads for those three categories from being targeted based on users’ gender, age, parental status, marital status, or ZIP code, it said in a blog post Thursday. Google added that it will also “provide housing advertisers with additional information about fair housing to help ensure they are acting in ways that support access to housing opportunities.” The policy update will be rolled out to advertisers across the United States and Canada in the coming months. Google’s new policy was crafted “working closely” with HUD, and it brings Google housing ads more in line with the Fair Housing Act.

On the surface, this sounds like a great idea. In practice, advertisers will develop proxy strategies that they won’t disclose, such as crafting an algorithm that uses a prospect’s credit score, where they went to school, some combination of the last three places they lived, etc.

Proxy data is bad because there is no feedback loop to improve it. If they can’t ask Google to directly cluster and classify an audience, sophisticated advertisers will get around the problem with proxy data. This is much worse than the problem this “policy” is trying to solve for because it makes the discrimination completely invisible — and unfixable. This is not the intended consequence of this policy change, but it will be the inevitable result.