People using an iPhone 5 need to update its software or their phone will stop working on Sunday.
Apple has warned that from 12am on Sunday, November 3, iPhone 5 owners won't be able to connect to the internet unless they have iOS 10.3.4.
Web browsing in Safari, emails, App Store, iCloud and maps will all go offline for people who don't keep their phone up to date.
Those with the iPhone 4S and various older iterations of the iPad will also need to update the software on their devices.
The problem has stemmed from a GPS issue which only occurs once every 19 years and happened in April, causing some devices to lose track of time.
When the GPS rollover happened in April, Apple had to push out a bug fix to stop devices' location services and clocks becoming confused.
Because of the way weeks are recorded in GPS systems, the date effectively resets to zero every 1,024 weeks – every 19.7 years.
The bug fixes were only applied to Apple software iOS 10.3.4 and iOS 9.3.6 and later, so anyone who hasn't updated will face serious problems, 9to5Mac reported.
Apple warned users of older devices in July that they had almost four months to update the software before Sunday's moment of reckoning arrives.
iPhone 5 owners have been receiving pop-up warnings on their phones telling them 'Action required for iPhone 5'.
Users must also upgrade the iPhone 4S, iPad 2, iPad with Retina Display and the fourth generation iPad.
In a release on its website Apple said: 'Starting just before 12:00 a.m. UTC on November 3, 2019, iPhone 5 will require an iOS update to maintain accurate GPS location and to continue to use functions that rely on correct date and time including App Store, iCloud, email, and web browsing.
'This is due to the GPS time rollover issue that began affecting GPS-enabled products from other manufacturers on April 6, 2019.
'Affected Apple devices are not impacted until just before 12:00 a.m. UTC on November 3, 2019.'
If the software isn't updated by the 3rd the only option will be to connect the phone to a computer and do it manually through desktop apps.
To update iPhone or iPad software, click Settings>General>Software Update.