Apple is launching iOS 11 today, which means millions of iPhone users are about to upgrade their device’s software. Every iOS update comes with a host of changes, but some are not immediately obvious. Apple upgraded millions of iOS devices to a new modern file system earlier this year, and today it’s starting to roll out a new image file format with iOS 11 that could be troublesome to Windows users.

High Efficiency Image File Format (HEIC) is a new image container format from the developers of MPEG, a popular audio and video compression standard. HEIC will be used by default on new photos on iOS 11, and it’s designed to save you storage space. As it’s a new container format, there will be some incompatibilities along the way, and Apple does a good job at handling most of these. iOS 11 will automatically share HEIC files as the default JPEG format for apps, so you won’t notice anything when you share a photo on Twitter or Instagram. iOS 11 also offers to automatically transfer photos and videos in a compatible format for Mac or PC users, useful if you’re simply plugging your iPhone into your laptop or PC.

Most iOS 11 users won’t notice any changes

While it’s a great improvement for iPhones with limited storage, it might cause you some issues with third-party photo apps that backup photos to cloud storage. If you have a work flow that relies on backing up pictures to Google Photos or Dropbox, then you might find that the images get stored in HEIC instead of JPEG. Google Photos and Dropbox both support HEIC within their apps, but Microsoft has been to slow to support the new format. Still, the latest version of OneDrive will automatically convert HEIC photos to JPEG before uploading them to the service. This means that although HEIC isn’t natively supported on Windows 10, you won't need a dedicated photo app or a method to convert files in order to view your iPhone photos on a PC. You'll be able to view them on OneDrive mobile apps, OneDrive.com, and in Windows 10. You can also turn off the feature by going to settings > advanced > upload most compatible feature.

If you're facing issues with other cloud services, an online converter is available, but be wary about what photos you’re sharing with random websites. The other option is to disable HEIC if you’re facing problems. This will force iOS 11 to store all images as JPEG. You can disable HEIC from settings > camera > formats, but if you’re not having issues then it’s worth keeping the high efficiency mode enabled to save space.

Update 9/19, 2:31 PM ET: Updated to reflect OneDrive's automatic HEIC to JPEG conversion.