A man's family was told to pay an excessive proportion of his care home costs after being wrongly financially assessed by Cornwall Council.
An ombudsman report said it believed there may be "systemic problems in the way Cornwall Council assesses people".
The council decided his whole pension should be used, when half should have been disregarded to cover his wife's costs.
It has apologised and said "we will be changing our approach".
The report from the Local Government and Social Care Ombudsman said the man, known as Mr X, died in January.
The Care and Support Regulations state that people who have more than £23,250 are expected to pay the full cost of their residential care home fees.
However, once their capital has reduced to less than this, they only have to pay an assessed contribution towards their fees.
Mr X's son twice appealed the council's assessment before taking it to the ombudsman.
The council has been ordered to pay £6,941 to Mr X's estate, and £250 to his son for "the time and trouble it has put him to pursuing this complaint".
Michael King, Local Government and Social Care Ombudsman, said: "I believe there may be systemic problems in the way Cornwall Council assesses people in the county.
"I have asked the council to identify anyone else adversely affected by similar issues over the past 12 months and provide them with a remedy too.
"I am disappointed the council has not yet agreed to do this, so I urge it to reconsider its position."
Cornwall Cornwall's portfolio holder for adults Rob Rotchell said: "We apologise to the individuals involved in this case for the distress caused.
"We will be changing our approach and our team will be taking account of these findings in carrying out assessments in the future.
"It may not be possible to comply with the recommendation relating to assessments already undertaken but we are looking into this and have raised this matter with the ombudsman."