When you go to vote for state legislators, you don’t expect that some other voters in your state will have their votes weighed double yours, just because they happen to be neighbors with people who can’t vote. But that, in effect, is what Texas is trying to do.

When Texas draws its state legislative districts, it looks only to equalize the total population in each district, ignoring how many of those people are actually citizens of voting age. The result is a plan that would create one senate district where 74% of the residents can vote and another where only 47% can vote. Depending on where you live, you might be one of 383,000 people who get to choose a senator, or one of 611,000.

This is a blatant violation of the principle of “one person, one vote” (OPOV) that the Supreme Court established 50 years ago under the Fourteenth Amendment’s Equal Protection Clause: no matter where you live in your state, your vote should have the same weight. Nonetheless, a three-judge federal district court upheld the plan, following a flawed Fifth Circuit precedent holding that the Equal Protection Clause was ambiguous as to whether total population or voter population should be equalized.

But if a state really only has to care about total population, it could create districts of 10%, 5%, or even 1% eligible voters—and the tiny groups of voters in those districts would each be able to choose one senator all the same. Cato, joined by the Reason Foundation, has filed an amicus brief in the Supreme Court arguing against this absurd result, focusing on rebuttals to two supposed justifications for allowing states to violate OPOV.

First, many have argued that the method by which members of Congress are apportioned to the states—according to total population—provides an important “federal analogy” that justifies using total population to allocate political power within a state. But history shows that the federal rule was created to solve a uniquely federal problem. Since states define suffrage for themselves, a rule based on eligible voters would provide states with a perverse incentive to expand suffrage as much as possible (for example, by lowering their voting age to 12) and thus artificially acquire more representatives.

States, however, are not mini-nations; one county in Texas cannot lower its voting age below that of the other counties in a bid to gain more state senators. The primary justification for the federal rule simply does not exist at the intra-state level. In fact, the true federal analogy is to that part of the Fourteenth Amendment which was designed to remove the newly freed but still disenfranchised slaves from their states’ apportionment total, so as not to give more voting power to their former owners. The Fourteenth Amendment confirms the principle that when unfranchised persons are not “virtually” represented by the votes of their neighbors, they should not be used to give more weight to the voting power of those neighbors.

Second, besides the misunderstood federal analogy, it has also been argued that Section 2 of the Voting Rights Act, as currently interpreted, requires states to gerrymander districts along racial lines in ways that will make low-percentage-voter districts inevitable. But a statute can’t trump the Equal Protection Clause. States should not be tied in knots with statutory requirements when drawing their districts such that OPOV is reduced to, at best, a secondary or tertiary consideration.

To the extent statutory barriers are preventing states from treating their voters equally, the Supreme Court must remove them. In this case, the Court should to equalize the weight of each vote.

The Supreme Court will hear the case of Evenwel v. Abbott late this fall.