When officials asked for the Welsh translation of a road sign, they thought the reply was what they needed.
Unfortunately, the e-mail response to Swansea council said in Welsh: "I am not in the office at the moment. Send any work to be translated".
So that was what went up under the English version which barred lorries from a road near a supermarket.
"When they're proofing signs, they should really use someone who speaks Welsh," said journalist Dylan Iorwerth.
Swansea council got lost in translation when it was looking to halt heavy goods vehicles using a road near an Asda store in the Morriston area.
All official road signs in Wales are bilingual, so the local authority e-mailed its in-house translation service for the Welsh version of: "No entry for heavy goods vehicles. Residential site only".
The reply duly came back and officials set the wheels in motion to create the large sign in both languages.
The notice went up and all seemed well - until Welsh speakers began pointing out the embarrassing error.
Welsh-language magazine Golwg was promptly sent photographs of the offending sign by a number of its readers.
Managing editor Mr Iorwerth said: "We've been running a series of these pictures over the past months.
"They're circulating among Welsh speakers because, unfortunately, it's all too common that things are not just badly translated, but are put together by people who have no idea about the language.
"It's good to see people trying to translate, but they should really ask for expert help.
"Everything these days seems to be written first in English and then translated.
"Ideally, they should be written separately in both languages."
A council spokeswoman said: "Our attention was drawn to the mistranslation of a sign at the junction of Clase Road and Pant-y-Blawd Road.
Other confusing signs
"We took it down as soon as we were made aware of it and a correct sign will be re-instated as soon as possible."
The blunder is not the only time Welsh has been translated incorrectly or put in the wrong place:
• Cyclists between Cardiff and Penarth in 2006 were left confused by a bilingual road sign telling them they had problems with an "inflamed bladder".
• In the same year, a sign for pedestrians in Cardiff reading 'Look Right' in English read 'Look Left' in Welsh.
• In 2006, a shared-faith school in Wrexham removed a sign which translated the Welsh for staff as "wooden stave".
• Football fans at a FA Cup tie between Oldham and Chasetown - two English teams - in 2005 were left scratching their heads after a Welsh-language hoarding was put up along the pitch. It should have gone to a match in Merthyr Tydfil.
• People living near an Aberdeenshire building site in 2006 were mystified when a sign apologising for the inconvenience was written in Welsh as well as English.