Smart meter users in England have been left confused after their readings randomly switched to Welsh.
Customers of Bulb energy have reported the switch in the language of their devices, despite some living more than 100 miles away from Wales.
The company said the "rare" glitch has affected about one in 200 of the meters.
But those hit by the error were also left scratching their heads trying to fix the problem - as the language of the device's settings menu had also changed.
Users noticed the switch after the "usage today" indicator changed to "defnydd heddiw".
Bulb posted a solution to the issue on its website after several customers complained.
A spokesman said: "In some rare cases, In-Home Displays switch to Welsh.
"While we think Welsh is a great language, we understand that in many cases people will want their display to be in English.
"Luckily the solution is just a few button presses away, and language settings can be changed in less than 10 seconds."
James Tombs, who lives in West Sussex, more than 100 miles from the Welsh border, told the Money Saving Expert website: "I don't live in Wales and don't know Welsh ... I went on to the Bulb forums, found others with the same problem and followed directions to change (the) language.
"It has been fine since."
For those wanting to switch it back to English, the company gave the following instructions:
- "Press the 'OK' button at the bottom of the In-Home Display, and then the right arrow button until you see 'Gosodiadau Wedi anfon yr'.
- "Press OK. This takes you to settings.
- "Press the right button until you see 'Dewis iaith Wedi anfon yr'. (If this doesn't work, you may need to try the next option, 'Clirio Gosodidau Wedi anfon yr').
- "Press OK.
- "Select English on the left, by pressing the left arrow, then 'OK'."