Pedestrians walk past a Capital One ATM outside of a bank branch in New York.

Capital One customers who saw double were not imagining it.

With a technical error causing debit transactions to post more than once to accounts, some customers were reporting negative balances due to the error.

Thursday morning, Capital One said in a tweet that the issue has been resolved and account balances should now be accurate. A spokeswoman also told CNBC that the problem was limited to some bank branches.

"Customers are being notified when they sign in to their accounts or contact us that their balances should now be accurate," said Amanda Landers, a Capital One spokeswoman. "Customer accounts have been credited for any inaccurate postings related to this issue."

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While the error apparently is resolved, the episode is a good reminder to consumers that monitoring your bank account for odd or incorrect charges is important.

"You should have online access to your bank account and check it on a regular basis," said Linda Sherry, director of national priorities for Consumer Action.

If you see something amiss, contact your bank immediately to resolve the issue.

Sherry said that for online purchases, it can be better to use a credit card instead of a debit card. Not only do you get fraud protection (which also typically comes with unauthorized debit charges) but it does not come straight out of your bank account the way a debit charge does.

Additionally, if you are able to sign up for overdraft protection — linking your account to a savings account or having an overdraft line of credit — you have backup cash in case something like this happens.