Hundreds of motorists are to be repaid their £60 speeding fines after a clerk realised temporary speed limit warning signs had been put in the wrong place.
Camera vans were sited at road works on the Wrexham bypass
The blunder means more than £68,000 will be given back to 1,100 drivers.
Speed cameras were placed at road works on the A483 Wrexham bypass, where the limit had been cut from 70mph to 40mph.
It is the latest controversy for North Wales Police area whose Chief Constable Richard Brunstrom is unapologetic over his hard-line stance against speeding.
Any points put on drivers' licences will also be removed.
The anti-speed scheme, Arrive Alive, which coordinates speeding clampdowns in north Wales, will send out letters in the next few days to 1,136 motorists, telling them that their fines will be reimbursed.
Mobile camera vans were positioned at the road works after contractors had requested them last October.
But the temporary speed limit signs were put in the wrong place and the mistake was not noticed until after prosecutions were brought.
A spokeswoman for Arrive Alive, which operates the cameras, said the traffic control was put in place under Welsh Assembly Government guidelines.
She said: "An officer working for the North Wales Road Casualty Reduction Partnership recently identified an error in the location of temporary signage on the A483 northbound road works.
"In consequence, the partnership has immediately effected the cancellation of all 1,136 notices issued at this location during the relevant time period from 6-28 October."
A solicitor firm acting for North Wales Police is dealing with the matter.
Last month, figures showed the numbers of motorists caught speeding on roads in north Wales had risen by 70% compared to the previous year.
Nearly 6,000 drivers were hit with £60 fines in March 2005 compared to 3,466 in March 2004.