Organisers of the Plusnet Yorkshire Marathon have made new places available for the October 20th 2013 race.
Event Director Sara Birkinshaw said "unprecedented demand" from members of the public meant capacity for the York 26-miler has been increased to 6,100.
"We knew the Plusnet Yorkshire Marathon would be popular, but I think it is fair to say it took even us by surprise when it sold out in just three days," she stated.
Ms Birkinshaw claimed it may have been possible to sell out the event twice over, pointing to the "enormous number" of requests received since January.
The additional marathon places will be released for sale at 9AM on Friday April 26th.
They will only be available to those registered on the official Plusnet Yorkshire Marathon waiting list - via theyorkshiremarathon.com - by midnight on Monday April 22nd.
The 2013 event will be the first staging of the Plusnet Yorkshire Marathon, sponsored by the Sheffield-based broadband provider.
A team of Plusnet employees will be among those participating, in a bid to raise money for Sheffield homeless charity Roundabout.