Olympic qualification for the marathon and road race walk events can restart from 1 September, three months earlier than previously announced, the sport's governing body World Athletics has ruled.
However, qualifying for all other track and field events at next year's Tokyo Games would remain suspended until 30 November as originally planned, it said in a statement.
Qualification was put on hold in early April due to the coronavirus pandemic which has caused the Games to be postponed for one year until July and August next year.
World Athletics president Sebastian Coe said the change was needed for road athletes due to a lack of qualifying opportunities.
"Most of the major marathons have already been cancelled or postponed for the remainder of this year and the evolution of the pandemic makes it difficult to predict if those scheduled for the first half of next year will be able to go ahead," Coe said.
"That situation, combined with the fact that endurance athletes in the marathon and race walks can only produce a very limited number of high-quality performances a year, would really narrow their qualifying window without this adjustment."
Organisers of the London Marathon, due to take place on 4 October, were prepared to help athletes from around the world travel to the event achieve an Olympic qualifying time, World Athletics said.
It was also working with organisers of the Abu Dhabi Marathon, scheduled for 11 December, to see if they could offer similar opportunities, and hoped there would be at least two race-walking events between September and November.
Fionnuala McCormack has qualified for the Women's Marathon in Tokyo next summer, which will be her fourth Games, while Paul Pollock, Kevin Seaward and Stephen Scullion, who rowed back on a retirement announcement earlier in July, have qualified for the Men's race.
In men's race walking, Alex Wright has booked his place at the Games for the 20km edition, with Brendan Boyce in the 50k.