"That's not very good news," Gordon Whalen, 85, told CBC News, describing a call he got last week saying he is among those will have to repay the government.
Finance Minister Ross Wiseman revealed last week that the government had inadvertently paid out almost $1 million in pension benefits, although he also said government wouldn't impose severe hardships on pensioners.
Whalen, however, said that any money he has to turn over to government will have a devastating effect on his limited finances.
"I won't be able to handle it, to pay it back," he said in an interview.
"I'll be 86 next month and I'm having a lot of trouble right now."
Whalen, who worked for 25 years as a firefighter, was told that he was overpaid $18 a month for 20 years. By CBC calculations, that means he would have to pay back more than $4,000.
Whalen and his wife live on pension income of less that $40,000 a year, including Canada Pension benefits, he said.
His health is failing. There's a pacemaker in his chest, he receives morphine, and he has diabetes.
"There's so many things now [to] try to keep things going, to pay your bills," he said.
'Sad to see it'
His daughter, Paula Hennebury, says her father deserves better.
"It's sad to see it, and I think it's wrong," she said, "to take something that he worked so hard for. There are a lot of people who are in the same health as my dad."
Whalen hopes his story makes people angry, and that they remember it when they vote in the next provincial election.
"I don't think the government should take the little bit that we have got," he said.
"There must be some sensible people in there. For ministers like Mr. Wiseman and our premier to do the like of this to the like of me, and others, there's something not right."