NASA has nixed the first all-female spacewalk over a spacesuit size issue.

Astronaut Anne McClain was supposed to float out of the International Space Station this Friday with newly arrived Christina Koch. But McClain pulled herself from the lineup because there's not enough time to get two medium suits ready. Koch will go out with a male crewmate.

NASA spokeswoman Brandi Dean said Tuesday that McClain trained in both medium and large spacesuits. She wore a medium for last Friday's spacewalk and was supposed to switch to a large this week, but decided a large would be too big.

In 54 years of spacewalking, women have only gone outside with men. That's because men have always outnumbered women in space.