Runners who took part in a half marathon in Shropshire say the course was about "half a mile" too short.
Emily Hunt, the second-placed woman in the Shrewsbury Half Marathon, noticed a problem when recording the route on her mobile phone app.
She praised Sunday's event but added: "To have a short route is kind of inexcusable because you can measure it in advance and get it right".
Organiser Dave Downes of In the Running said he was investigating the matter.
About 1,500 runners took part in the event, including experienced club runners and fun runners. The race, which started and ended at the County Showground, weaved through Shropshire's countryside and past Shrewsbury Cathedral and the Quarry.
But collective curiosity was raised when runners revealed they had greatly reduced their personal best times, with some taking to social media to complain the course fell short of the official 13.1m distance.
It is believed part of the course was missed out by the racers, with one man saying there were two sections where the runners were being sent down the wrong route.
Ms Hunt said: "It's something that could have been avoided.
"Sometimes you do get hiccups when you stage these sort of races and I think there's a lot to recommend the Shrewsbury Half. The marshals were brilliant, there were lots of water stations and actually it was a cracking route with lots of support and atmosphere."
Lee Smith wrote on Twitter: "Chuffed with my Shrewsbury Half PB but will be gutted if it wasn't a full Half" and Mathew Dobbie wrote: "#Shrewsburyhalf my Garmin and wife's TomTom, half mile short. Wife's 1st marathon and she is gutted #unacceptable".