Your iPhone will crash if it receives a text message containing just one letter, Apple has admitted. The tech giant is urgently working to fix a bug which brings the device to its knees when a single character in Telugu, an Indian language, is sent to the device or typed in its text editor.

The problem also affects the software which powers Mac computers, Apple Watches and Apple TV devices. Older versions were not affected by the bug and Apple said it has already fixed the issue in the current beta versions of the operating systems. Devices running on iOS 11 crash when any application receives the character, The Verge reported.

It causes apps to become unresponsive, including Apple’s iMessage and third-party applications like WhatsApp, Gmail and Facebook messenger. However, some apps like Telegram and Skype seem to be unaffected. You can see the dangerous letter in the tweet below.