BIDDEFORD — Organizers of a Maine marathon are apologizing for a course error that caused many runners to go an extra half-mile, costing some a chance to run in next year’s Boston Marathon.

Officials with the Maine Coast Marathon say some runners in Sunday’s race were mistakenly directed down a dead end before looping back, bringing their total distance to about 26.7 miles. The error caused some Boston hopefuls to post times that are unlikely to qualify.

The course was corrected but, because not all runners ran the extra distance, officials say they can’t simply adjust the times.

Race director Charles Melton said they will offer refunds to those who missed qualifying for Boston because of the mistake.