Two astronauts—both women—were slated to make history on March 29 by participating in the first all-female spacewalk. Then their wardrobe got in the way.

According to the BBC, NASA had to cancel the planned event at the International Space Station because of sizing issues related to one of the necessary spacesuits. It was discovered a little too late that both astronauts—Christina Koch and Anne McClain—needed spacesuits with a medium-sized hard upper torso. However, only one of the two medium-sized suits had been configured for a spacewalk. So instead of McClain stepping into outer space to install batteries at the space station, a male colleague, Nick Hague, will take her place alongside Koch.

"Anne trained in 'M' and 'L' and thought she could use a large but decided after [last] Friday's spacewalk a medium fits better," said Stephanie Schierholz, a NASA spokesperson. "In this case, it's easier (and faster!) to change space-walkers than reconfigure the spacesuit."

Part of the problem is that it's hard to find a proper fit before an astronaut has actually been in space. "Individuals' sizing needs may change when they are [in] orbit, in response to the changes living in microgravity can bring about in a body," Brandi Dean, a spokesperson for the Johnson Space Center in Houston, told the AFP.

In this case, McClain only learned she needed a smaller size while doing an actual spacewalk last Friday, making her the 13th woman to achieve this milestone. Koch will become the 14th woman during her planned spacewalk this week.

The news comes just two weeks after the head of NASA made headlines for stating that the first astronaut on Mars would likely be a woman. NASA administrator Jim Bridenstine also said a woman would likely be the next person to set foot on the Moon.

[h/t BBC]