WASHINGTON ― Republicans wrote their massive tax legislation in such a rush that even before they’ve sent it to the president’s desk, they’re already talking about writing another bill to fix all the mistakes in the first one.

Rep. Kevin Brady (R-Texas), the lead author of the tax legislation in the House of Representatives, said Friday that he expected Congress would need to draft another bill to make “technical corrections.”

“I can’t imagine any major undertaking like this that doesn’t require technical corrections in the future,” Brady told reporters.

Republicans have repeatedly adjusted major provisions of their legislation over the past several weeks. The final version of the bill released Friday contained yet more significant changes to a business deduction that tax experts have warned could result in a lot of creative accounting and unintended consequences.

Technical corrections to major legislation are indeed common, but usually they aim to fix errors that lawmakers discover after passing a bill ― not ones they assume exist beforehand.

Steven Rosenthal, a lawyer and tax expert who formerly worked for the congressional Joint Committee on Taxation, said he was not aware of any other instance in which lawmakers anticipated technical corrections for tax legislation that had not even been enacted.

“This legislation is tax policy malfeasance,” Rosenthal said.

Brady said he hoped Democrats would go along with fixing the tax bill post-passage ― a curious request since it wasn’t so long ago that Republicans wanted nothing to do with corrections for another piece of major legislation: the Affordable Care Act.

Obamacare contained drafting errors and mistakes, including one that nearly proved devastating to the law’s implementation ― a passage that didn’t specify whether tax credits for buying health insurance should be available in all states or just some. A simple one- or two-word change to the law’s language would have cleared up the ambiguity. Rather than working with Democrats to enact such a measure, so that it had the votes to pass Congress, Republicans supported a lawsuit that, if successful, would have cut off the tax credits for millions ― leaving most of them with no health insurance at all.

The case went all the way to the Supreme Court, which slapped it down by a 6-3 vote. But that history may loom large if or when Republicans turn to crafting technical fixes for the tax bill.

GOP lawmakers are enacting the tax bill itself through the budget reconciliation process, which means that it can pass with a simple majority and no threat of a filibuster ― an essential requirement for the Republicans, because they have only 52 seats in the Senate now and that drops to 51 once Doug Jones takes the Alabama seat now occupied by a Republican. But a bill fixing the tax legislation next year would not necessarily have the same advantage of the lower Senate vote threshold, meaning Republicans could need Senate Democrats to get it done.

“We can do even more to improve this tax code,” Brady said. “I’m hopeful Democrats, who’ve always said they’re for tax reform but today are defending the status quo, I hope they rethink that and work with us to improve the code.”

As congressional committees have written and rewritten parts of the GOP legislation over the past month, lobbyists and tax experts have already identified multiple apparent drafting errors that Republicans subsequently fixed, such as a mistake in the Senate bill that could have allowed employees to claim a deduction intended only for business owners. But it’s not just additional little mistakes that Republicans might need to address going forward. There could be major substantive problems, too, because of policy choices made in the hasty construction of the bill.

For instance, the House and Senate bills both eliminated deductions for state and local income taxes, but allowed filers to continue deducting what they pay in property taxes up to a $10,000 limit. The new joint bill, which combines the House and Senate versions, would allow filers to deduct a mix of property and income taxes up to that same amount.

Limiting deductions is important because that offsets federal revenue loss, by more than $600 billion over 10 years, from the lower tax rates and other breaks in the legislation. But state governments, to defend their own budgets, could take actions that undermine that tradeoff.

The effort to curb state and local tax deductions in particular would put pressure on states, since they could lose political support for taxes that can no longer be deducted on voters’ federal tax returns. States might protect their revenue by reducing taxes on individual income and property while increasing taxes on business payrolls, which businesses could still deduct. And since the joint tax legislation would still let individuals take deductions for charitable donations, states might let people make deductible “donations” in exchange for a state tax credit.

“Many states already have laws in place granting state income tax credits for donations to certain funds, and the IRS has allowed taxpayers who take advantage of these credits to deduct their payments as charitable contributions rather than as state taxes,” a group of tax scholars wrote in a paper published Monday, “The Games They Will Play,” which identifies a wide array of tax avoidance ploys that could be fostered by the GOP tax bill.

If states simply shift how they gather taxes, and households and businesses wind up deducting as much in local levies from their federal tax returns as they do currently, then the tax legislation would increase federal budget deficits by $600 billion more than Republicans intend.

But Darien Shanske, a tax professor at the University of California Davis School of Law and one of the scholars who wrote that paper, suggested that the potential revenue loss is not necessarily something Republicans would act to “fix,” given that their legislation would already add more than $1 trillion to the national debt.

“They clearly don’t care about the deficit,” Shanske said.

The provision that’s probably gone through the most mutations, and the one experts say is ripest for abuse, is a new deduction for certain types of business income.

Republicans wanted to cut business taxes, but since most commercial enterprises aren’t taxed as corporations, cutting corporate tax rates wasn’t enough. So lawmakers added a tax break for owners of “pass through” firms whose business income is taxed on their individual returns ― a deduction worth 20 percent of qualified business income. If those kinds of firms end up paying a much lower effective tax rate than wealthy individuals do, high earners will have a strong incentive to find a way to reclassify their personal income as business profit.

People with high incomes could turn themselves into pass-through business entities for tax purposes, despite provisions of the legislation that Republicans describe as “guardrails” to prevent such gaming. The Senate bill had a list of business types not eligible for the new break, including doctors, lawyers, engineers, architects or “any trade or business where the principal asset of such trade or business is the reputation or skill of one or more of its employees.”

The final bill resembles the Senate version, but for some unknown reason, engineers and architects have been removed from the list of those restricted from taking the full deduction. The final bill also contains a new provision allowing pass-through companies to count the value of physical property toward their deduction ― an apparent gift to the real estate industry.

Sorting out what type of businesses qualify for the pass-through deduction will be a major challenge for the Internal Revenue Service, one compounded by budget constraints and a short timeline. Republicans aim to pass the law this week, and then it would go into effect Jan. 1.

“The concept of allowing lower tax rates on income that passes through a partnership or that is earned by an independent contractor is completely novel,” Rosenthal said. “This experiment is completely untested.”