The United Kingdom’s highest court ruled Wednesday that the legal definition of “woman” is based on biology and does not include trans-identifying men who say they are women.

In the landmark judgment, the British Supreme Court ruled that the meaning of “woman” in equality legislation is a “biological woman and biological sex,” and the “concept of sex is binary, a person is either a woman or a man.”

The ruling is a watershed moment in Britain’s shift on gender ideology, which has faced a referendum in Europe in recent years, especially as the harms of transgender drugs and procedures on children have come to light and sparked legal challenges.

The court case was about whether trans-identifying men with a “gender recognition certificate” that legally recognizes them as female are protected from discrimination as a woman under the 2010 Equality Act.

The court ultimately ruled that interpreting sex as simply as what someone’s gender certificate says would be “incoherent,” according to a summary of the ruling.

“The terms woman and sex in the Equality Act 2010 refer to a biological woman and biological sex,” Lord Patrick Hodge, one of the court’s senior judges, told the court. “The provisions relating to sex discrimination can only be interpreted as referring to biological sex.”

The five judges cautioned that they were not ruling broadly on whether trans-identifying men were women, saying that was beyond the role of the court.

Lord Hodge said the ruling should not be seen as “a triumph for one or more groups in our society at the expense of another – it is not.”

Critics of gender ideology were ecstatic nonetheless.

A group called For Women Scotland filed a challenge in 2018, butting heads with the Scottish government, which argued that trans-identifying men were legally women.

For Women Scotland celebrated with tears and hugs in the courtroom before a victorious exit, where they cracked open a bottle of champagne outside with other campaigners against gender ideology.

Other groups celebrated as well.

“The court has given the right answer: the protected characteristic of sex – male and female – refers to reality, not paperwork,” the group Sex Matters said.

The LGB Alliance, which presented arguments in court, called the ruling a “watershed for women.”

In response to the ruling, the British government said it supports “single-sex spaces.”

“This ruling brings clarity and confidence, for women and service providers such as hospitals, refuges, and sports clubs,” a British government spokesperson said. “Single-sex spaces are protected in law and will always be protected by this Government.”