Small companies have been experimenting with a four-day workweek, for some time. Now, Microsoft has proven that the same model works for bigger businesses.

This summer, the company’s Japan office introduced a summer program called “Work Life Choice Challenge,” in which its offices were closed every Friday in August, giving employees an extra day off, CNN Business reports.

Microsoft saw astronomical results from the initiative: productivity—which was measured by sales per employee—grew by almost 40% compared to the same period last year. Over 90% of Microsoft’s 2,280 employees in Japan said they were affected by the new measures. The program also allowed the company to save on other resources, like electricity.

The initiative was especially important for Japan, which struggles with a culture of overwork. The problem is so bad that the country has created a term for it. "Karoshi" means death by overwork from stress-induced illnesses or severe depression.

The issue made headlines in 2015, when an employee at a huge Japanese advertising firm committed suicide on Christmas Day. Authorities later said the staffer was working excessive overtime. Two years later, a Japanese reporter also died from working long hours, clocking in 159 hours of overtime the month before her death.

Some companies have given their employees more flexibility, and the government started a campaign called “Premium Friday,” which encourages employees to leave early every last Friday of the month.

Microsoft is set to try the program again later this year and will ask other companies to join in.