Cyclists were left confused by a bilingual road sign telling them they had problems with an inflamed bladder.
Safety message in English or health warning in Welsh?
The "cyclists dismount" sign between Penarth and Cardiff became "llid y bledren dymchwelyd" in Welsh - literally "bladder inflammation upset" (or tip or overturn).
The Vale of Glamorgan Council said new signs were being made.
It is possible that an online translation led to confusion between cyclists and cystitis.
The temporary sign at roadworks is to be replaced.
Welsh-speaking cyclist Matt Lloyd, 27, said: "When I read the sign I thought someone was having a laugh. I've never even had a bladder disease."
Welsh language expert Owain Sgiv told the South Wales Echo: "It certainly does not mean anything like cyclists dismount."
A spokesman for the Vale of Glamorgan Council's highways department said: "A mistake has been made and we are investigating.
"Amended signs are being made and will be put up as soon as possible".