When it premiered in 1966, Star Trek presented a world unlike anything else on television at the time. But there was one frontier even its creator wouldn’t venture into: As Entertainment Weekly reports, the word "God" must never be mentioned on the show.

The rule originated with Star Trek’s creator, Gene Roddenberry, and will be followed by the makers of the franchise’s newest property, Star Trek: Discovery, which premieres in September. According to the writer Kirsten Beyer, the new series adheres to Roddenberry’s idea of "a science-driven 23rd-century future where religion basically no longer exists." That doesn’t just mean that religion shouldn’t interfere with the plot; even a casual "for God’s sake" ad libbed by an actor won't make it into a final cut.

Roddenberry was known for creating several cardinal rules for the Star Trek universe. Besides forbidding any mention of religion, he also maintained that crews should be diverse, characters should avoid meddling with other cultures, and there should be no serious interpersonal conflicts aboard the vessel (you can read more about his vision in the Star Trek: The Next Generation show bible [PDF]). But even the showrunners of Star Trek: Discovery don’t promise to stay 100 percent faithful to Roddenberry’s wishes. They’ve already stated that they’re abandoning his rule about conflict in favor of more realistic drama. So if their position on the God rule changes, it won’t be unprecedented.

[h/t Entertainment Weekly]