This past weekend, the most dysfunctional state legislature in America passed a landmark same-sex marriage bill. New York is now the largest state in the country to legalize gay marriage—and thanks to a late-breaking vote in the State Assembly, it will have the largest “transit lockbox” in America (assuming New York Governor Andrew Cuomo signs the bill into law). At least theoretically. As transportation nation explains:

Here’s an official description of [the bill], followed by an English translation:

“Prohibits diversion of resources from dedicated funds derived from taxes and fees that support the MTA, the NYC transit authority and their subsidiaries in certain instances.”

That’s addressed to past, present and future governors of New York. What it’s saying, roughly, is no more raiding the NY MTA’s budget to plug up state shortfalls.

The authority gets a crucial part of its revenues from a percentage of business and real estate taxes. Since 2009, as the recession reduced that income, the state took away an additional $260 million from those dedicated funds. The lockbox bill is designed to prevent that. Advocates say protecting NY MTA coffers will reduce the likelihood of a repeat of last year’s painful fare increases and service cuts.

Now in reality, the New York legislature can “raid the NY MTA’s” budget in all sorts of other ways, such as getting rid of taxes that fund the city’s subway, bus and commuter rail systems. Luckily the State Senate’s attempt at repealing the MTA-dedicated payroll tax was blocked by the legislature’s lower house. Even so, this bill doesn’t guarantee that the legislature won’t continue to misallocate resources, as the example of another, high-profile “transit lockbox” bills makes clear—in Maryland, a sales tax exemption effectively cancels out what many drivers would pay into the state’s public transit lockbox.

Could the New York lockbox fall victim in a similar accounting trick? Maybe. The New York law still allows the state to raid non-dedicated transit funding. As this Streetsblog post explains, money from the state’s general fund accounts for a trifling percentage of MTA revenue. But in a time of potential budget austerity (and deep state debt), it’s not hard to envision lawmakers reassessing the feasibility of forking over $4.5 billion a year in dedicated tax revenue, a situation that would force the state to either create new taxes and fees or subsidize more of the MTA from its general fund. Basically, this is a lockbox until lawmakers decide it isn’t anymore.

But it’s also an exciting and possibly historic development that has the potential to restore close to $200 million in annual funding to the MTA. Governor Cuomo should certainly sign the transit lockbox bill into law. At the same time, transit advocates shouldn’t grow complacent. Just because revenue from a deeply unpopular payroll tax has been put in a “lockbox” doesn’t mean that revenue is totally safe.