Some people love their money so much they don’t even tell their partner about it.

One in five people in a live-in relationship admit to “financial infidelity” — keeping a private bank account or credit card without telling a partner, according to a study released Monday by CreditCards.com. The survey of 2,000 people found 31% of millennials, 24% of people ages 38 to 53, and 17% of baby boomers have at some point had an account they keep secret from a partner.

Lying about having private accounts is actually more common than many people think, said Kimberly Palmer personal finance expert at NerdWallet. “People are often embarrassed about the money choices they are making, or they want to have a slush fund of spending money they can use without asking permission,” she said.

Although the practice may be common, that doesn’t mean it’s widely-accepted: 31% of those in a relationship think that keeping a credit card, checking account or savings account secret from a partner is worse than cheating physically. “Keeping financial secrets in a relationship, just like any other type of infidelity, is a sure-fire way to spark an argument,” Matt Schulz, senior industry analyst at CreditCards.com said.

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People in relationships often have good reason to hide their financial issues: People can judgmental: 40% of Americans saying they wouldn’t date someone who had a bad credit score. Women were nearly three times as likely to consider credit score a major influence on a potential partner compared to men (20% versus 7%). More than half of Americans would not marry someone with significant debt.

Everything, of course, is relative. Financial infidelity can be defined differently by different people, Palmer says, and have varying consequences: Keeping a private credit card account so you can buy your husband gifts without his knowing is different than hiding a low credit score or thousands of dollars in debt. Because of this, couples need to be honest about their financial issues preferably before they move in together and, certainly, before they marry.

The good news: More people have the conversation about their finances before they set up house. Some 30% of couples who do not live together say they have never discussed their combined finances compared to just 11% of those who do live under the same roof. “People experiencing this need to set aside some time for an honest and difficult conversation,” Palmer said. “If you’ve been keeping secrets from your partner, it will do you both good to come clean.”