It happened to Kelly Zimmerman, an Ohio mom who did what she could to make sure her baby's seat was firm and secure.
"First I tried putting pool noodles underneath it to level it out, then resorted to using a rolled-up towel," she said. "It works, but it really doesn't give you much peace of mind as a parent."
Dr. John Bolte, an associate professor at Ohio State University College of Medicine, said a lot of parents are just like Zimmerman, and they struggle to find the perfect seat for their car.
Bolte and a team of researchers tried to match up 3,186 combinations of car seats and vehicles, and although car seats are made to protect your child, it doesn't mean that every seat fits every vehicle. So Bolte says using a towel to secure the baby's seat, like Zimmerman did, is a pretty normal thing to do.
"Actually, it's very common for car seat manufacturers to suggest homemade modifications like that," said Bolte. "All car seats you buy are safe, but not all of them may fit into your particular car."
Make it tight
According to the folks at DMV.org, parents should make sure they're pulling the seatbelt as tightly as possible around the seat to hold it in place.
If the seatbelt strap or harness can be moved, then you'll want to use a little more strength to pull it in tighter, and you'll do this by putting your knee into the seat for leverage. From there, pull the straps as tight as you can and it should secure the seat much better.
In addition, experts say to make sure the seat belt is straight and it doesn't have any kinks, and you should do all of these things before reaching for an object to hold the seat in place.
"If there is a gap between the buckle and your child's groin, try placing a rolled washcloth or diaper in the space for a more secure fit," says the DMV.org site, which despite its name is not affiliated with any government agency. "But only do this after the child has been securely fastened into the car seat."
Experts at KidsHealth.org remind parents to select a seat that has a label that says it meets or exceeds Federal Motor Vehicle Safety Standard 213, and by all means, avoid using used car seats.
If you do happen to get a used car seat, you should communicate with the manufacturer to see if there were any recalls, and you can also ask the manufacturer how much longer you'll be able to use the seat without putting your baby in danger.
Experts say never use a car seat that's more than six years old or use one that was already in a crash.
But even then ...
And Bolte says you should measure the inside of your vehicle before buying a car seat and you should never buy one willy-nilly.
"Car seats themselves are safe," he says. "They may just not fit properly in a particular car. We want caregivers to consider taking a few measurements and note some key dimensions of their vehicle before making a decision about a car seat. Taking a few measurements might save a child's life."
And experts say children should sit in a rear-facing car seat until they're either two years of age or until they reach the maximum weight limit for their seat.
"Many parents transition their child to forward-facing car seats too early because they believe that their child has outgrown the rear-facing car seat and the child is too large to be comfortable in that configuration," said Bolte.
"Based on the preliminary data of this study, comfort scores are similar for rear and forward-facing car seats and support the extended use of rear-facing car seats. Caregivers should always choose the option that is safest for their child."
Other experts stress to read the car seat's manual before you install it and make sure the seat doesn't recline any more than a 45-degree angle.
And if you're ever unsure if you've installed a seat correctly, you can visit a car seat inspection site in your area or go to the National Highway Traffic Safety Administration's website to find a site close to your home.