Tonight’s episode of Star Trek: Discovery referenced not only Star Trek’s past by mentioning Spock by name but also the future by revealing some surprising technology from the era of Star Trek: The Next Generation.

SPOILERS for Star Trek: Discovery episode 6, “Lethe,” follow.

Tonight’s Star Trek: Discovery included a scene in which Captain Gabriel Lorca and Ash Tyler, who just escaped a Klingon prison ship in last week’s episode, appeared to be in combat with the Klingons again. However, this time they appeared to be greatly outnumbered and yet somehow much more casual about their mission.

That’s because, as revealed at the end of the mission, this entire encounter was a holographic simulation taking place on the USS Discovery’s holodeck.

The holodeck is an iconic piece of technology from the Star Trek franchise, but one that wasn’t a part of Starfleet ships until the 24th century, the era of Star Trek: The Next Generation, Deep Space Nine, and Voyager. That makes it somewhat surprising to see a holodeck in use on Star Trek: Discovery, which is a prequel to Star Trek: The Original Series taking place in the 23rd century.

The Star Trek: Voyager episode “Flashback” established that Starfleet ships did not have holodecks on board until the late 24th century, though the crew of the Enterprise NX-01 encountered holodeck technology on a Xyrillian ship in the 22nd century. However, Star Trek creator Gene Roddenberry wanted to add the holodeck to the original Enterprise in The Original Series, but couldn’t due to budget restraints.

Roddenberry remedied that problem the Star Trek: The Animated Series episode “The Practical Joker,” which introduced the holodeck concept, though it only referred to it as a “recreation room.” However, whether The Animated Series is actually canon or not is still unclear. For a time, it was removed from canon, and Star Trek: The Next Generation writers were specifically told to forget about “The Practical Jokers” when they introduced the live-action holodeck on the Enterprise-D.

Star Trek: Discovery has already referenced Star Trek: The Animated Series twice, first by bringing up how Spock’s mother loved Lewis Carroll and then again by listing Robert April among the most-decorated captains in Starfleet history. However, neither of those specific points contradicted anything in established Star Trek canon. The existence of a holodeck on the Discovery, though in-line with The Animated Series, does directly contradict Voyager, though perhaps it can be dismissed as a unique feature of the Discovery since the ship is an advanced science vessel with a first-of-its-kind spore drive engine.

New Star Trek: Discovery episodes become available to stream Sundays at 8:30 p.m. ET on CBS All Access.