Mark April 6, 2019 on your calendar. It’s the date that some GPS units could stop working right.

Why? Well, it’s a lot like back in 1999 when some devices didn’t have the capability to roll over to the year 2000. It turns out that some GPS devices aren’t capable of rolling over to April the 7th.

Here’s why: Older GPS units measure the week number using a system that ranges from 0 to 1023. The date-keeping started back in August of 1999 and is now about to roll around to week 1024. Testing by the Department of Homeland Security found that some devices will get confused and roll back their clocks to 1980. Having an accurate time is a key part of how a GPS system determines locations.

Make sure the firmware is up-to-date in your GPS device. It also doesn’t hurt to check with the manufacturer to make sure your model won’t be affected.