For the iPhone, January 1, 1970 was not a good day.

There's a bug that will render modern iPhones, iPads, and iPod touch models useless. All you have to do to turn your expensive iOS device into a brick is set its clock to the aforementioned date.

The bug started receiving attention on Reddit Thursday with people experimenting on their own iOS devices to see if it worked. Some recorded the process, which involves changing the date in the Settings app and rebooting the device, and shared videos on YouTube:

It's unclear what causes Apple's operating system to crash from changing the date, but one proposed explanation is that it has something to do with changing time zones. Susceptible devices run Apple's A7 processor and later, starting with the iPhone 5s, iPad Air, and the second generation iPad mini.

"In some time zones, setting the date to 1 Jan 1970 will set the internal clock to a number less than zero, as the time is stored in GMT (as the number of seconds since midnight on that date) and then the offset is applied before display," wrote one Reddit user. "In other time zones, setting the clock will result in a positive time value. Best guess is that this is triggered by having the time value less than zero."

Manually restoring the device through iTunes doesn't work, so the only fix for victims of the bug is to pay a visit to their local Apple store.

This isn't the first clock-related bug to cause problems for the iPhone. Several bugs over the years have shut off or delayed alarms, causing people to be late to work.

Apple declined to comment.