If you’re like me, you rent your car with a credit card. And there are a lot of credit card companies out there that tell you that if you rent your car with their credit card, you’re covered for all other sorts of things like insurance, collision, and damage. Is that true? Not necessarily.

Adding a liability waiver to a rental car usually tacks on an additional $10 to $20 a day. If you can avoid it, that’s a significant savings. But it may have you rely on credit card coverage instead.

In order for your credit card coverage to be activated, you have to officially decline the supplemental coverage offered by the rental company. More importantly, you must use that credit card to pay for the rental. But even then, you might not be completely safe.

Be aware that with some credit cards, there are often entire countries where the coverage is null and void such as Ireland and Jamaica. So be sure to check. Some cards do fare better than others.

A study from WalletHub said Visa ranked the highest when it comes to coverage, followed by Discover, American Express, and Mastercard. Mastercard, for example, won’t cover accidents that take place on dirt or gravel roads.

Both Visa and Mastercard require roads be regularly maintained by the government to fall under their protection. Translation: an accident on a country road or mountain drive could cost you. And here’s a big reason you may choose to not use your credit card coverage altogether. It’s called the “loss of use fee.” That’s a fee levied by the car rental company for the days that the car is out of commission. For example, this fee could happen if the car is in the shop getting repaired after an accident.

So how can you avoid this? Before you even leave for your trip, ask your own auto insurance provider if you can add non-ownership coverage, which would cover that loss of use fee, and it may even lower your deductible if the car is damaged. But keep in mind that many policies are only effective for up to 15 days for domestic rentals and 31 days internationally.

Here’s the bottom line: don’t just have a conversation with your rental car company. You should also have a conversation with your credit card company. Have the company show you the language in its policy that shows you whether you’re covered as well as what you’re covered for. Then print out a copy and take it with you to the rental car counter before you ever agree to the rental car company’s insurance.

By Peter Greenberg for PeterGreenberg.com