Lieutenant Norishige Kanai is "relieved" he will be able to fit into the Soyuz capsule for the return to earth.
Lieutenant Norishige Kanai, currently living on board the International Space Centre (ISS), said on Twitter on Wednesday that he had in fact grown 2cm in height since arriving in space three weeks ago.
He measured himself to check his height again after his captain, Anton Shkaplerov, raised questions about his apparent growth spurt.
Lt Kanai, 41, on Tuesday had expressed his concern about the amount he had grown and whether he would be able to fit into the Soyuz capsule for his return back to earth at the end of the almost six-month mission.
His tweet in Japanese read: "This mis-measurement appears to have become a big deal, so I must apologise for this terrible fake news.
"My hip and back don't hurt, instead it seems the shoulder stiffness has gone away, so I don't think I have grown 9 centimetres. Thank you to veteran astronaut Shkaplerov (for pointing out my mistake).
It is common for astronauts to grow a few inches while in space as their spines extend due to the absence gravity, but this extra height disappears once they are back under the gravitational pull of the Earth's surface.
Lt Kanai launched as the Japan Aerospace Exploration Agency's crew representative on Expedition 54 to the ISS in December.