It’s not yet clear what may have caused the glitch, or when a repaired version of the update will be available.

Apple’s only statement on the subject, published by CNET, reads:

Due to a small number of Apple Watch customers experiencing an issue while installing watchOS 5.1 today, we’ve pulled back the software update as a precaution. Any customers impacted should contact AppleCare, but no action is required if the update installed successfully. We are working on a fix for an upcoming software update.

📬 Sign up for the Daily Brief

Our free, fast, and fun briefing on the global economy, delivered every weekday morning.