It’s not every day that a drug maker complains the FDA widened a market for one of its drugs. But this is what Ostuka Pharmaceuticals is doing in a lawsuit claiming the agency illegally broadened the indication for its best-selling Abilify antipsychotic, unfairly opening the door to generic competition in the process.

And the outcome could allow generic versions of Abilify on the market much sooner than Otsuka had expected, affecting the fortunes of the Japanese drug maker, which is trying to expand its presence in the lucrative U.S. market.

Here’s the background: Last December, the FDA approved Abilify for treating children with Tourette syndrome, a neurological disorder that causes tics. Otsuka welcomed the move, because its pill was scheduled to face generic competition next month, when the Abilify patent is set to expire.

This delayed generics, though, because the new indication gave Otsuka another seven years of exclusive marketing rights. That’s because of a so-called orphan designation, which refers to a drug used to treat a rare malady. This meant generic versions of Abilify could not appear until December 2021.

But last month, the FDA amended its decision by notifying Otsuka that the added indication for treating Tourette would apply to adults as well as children. By broadening the indication to include adults, Otsuka argues the FDA would trigger a labeling change that would usher in the arrival of generics.