Kuipers revealed on Wednesday that in trying to make a call—by pressing 9 and then 011 for an international line—he missed a crucial number, triggering an alert at NASA’s Johnson Space Center in Houston, Texas.

“The next day I received an email message: Did you call 911?” Kuipers, a 60-year-old astronaut with the European Space Agency, told Dutch radio show Met Het Oog Op Morgen.