Daniel Radcliffe, star of the Harry Potter films, has spoken out against author J.K. Rowling’s transphobic Twitter rant that mocked a headline using the phrase “people who menstruate.”

In a blog post for The Trevor Project, a nonprofit that works to prevent suicide among LGBTQ youth, Radcliffe rejected Rowling’s tweets and affirmed the need to support transgender youth. “Transgender women are women,” Radcliffe wrote. “Any statement to the contrary erases the identity and dignity of transgender people and goes against all advice given by professional health care associations who have far more expertise on this subject matter than either Jo or I.”

Radcliffe has a long history of working with The Trevor Project, having made major donations to the organization. He was the 2011 recipient of the organization’s Hero Award.