It’s important to check your credit score regularly, as the summary score is used to ascertain your creditworthiness — how often you pay your bills on time and how much you pay — and can determine interest rates, credit limits, and whether or not you can rent an apartment or get a loan.

Since credit scores can contain errors, it’s even more important to check them several times a year. Some experts recommend checking each of the three major companies, Experian, Equifax and TransUnion, once a year, or every four months, since you only can check each once a year for free.

John Oliver took those three to task on his show Sunday for their high error rates — as many as 1 in 5 people, or 20 percent. They have the highest number of complaints recorded at the Consumer Financial Protection Bureau, the group Elizabeth Warren originally proposed in 2007 and help create in 2010 in the wake of the Dodd-Frank Act.

However, even an error rate of 5 percent, according to a Federal Trade Commission report, means millions of people are affected. And that means their lives could be ruined, if a faulty credit report prevents them from getting a job, home, or business loan.

Oliver rips the error-prone companies apart and then skewers them with a prank. Watch below.

Screengrab via Last Week Tonight/YouTube