With its red-brick spire and stained-glass windows, St Johannes looks like any other 19th-Century Protestant church.
The room is being rented from the parish, while the church remains active.
But the mosque is not unusual because of its location. Rather, because of the people who come here.
At Berlin's newest mosque, men and women pray together, women are allowed to lead Friday prayers, and gay, lesbian and transgender people are welcome.
"Our mosque is open for everybody," says mosque founder Seyran Ates, a German Turkish-born lawyer and women's rights activist.
"And we mean that really seriously: everybody, every lifestyle. We are not God. We don't decide who's a good or a bad Muslim. Anybody can come through this door - whether you are heterosexual or homosexual, we don't care, it's not our right to ask."
Read more: The Berlin mosque breaking Islamic taboos - BBC News