I will confess: I am a car seat safety fanatic. Some people might call me an advocate, but let’s be real. I verge on crazy status.

I kept my kids rear-facing well past the age of two. I’ve schlepped their car seats on and off of airplanes more times than I can count. I’ve checked their car seat installation again and again until it is JUST RIGHT. Yes, I am that mama. But, I make no apologies. Why should I? If there’s one thing I’m crazy about, it’s my kids’ safety.

That’s why I was surprised—no, shocked—to discover that a car seat safety rule exists that I didn’t know about. As a result, I was unknowingly putting my son in an unsafe position.

You’re probably already familiar with the LATCH safety system. LATCH is an acronym for Lower Anchors and Tethers for Children and is the preferred method for installing your car seat. These are the anchor points in your car that allow you to clip your car seat directly into the frame of your car’s existing seat.

For years, since my oldest was born, I have been obsessive about always using the LATCH system. When we shuffle the car seats around, I always situate the kids’ in the seats with a LATCH system, even when it makes for undesirable seating combinations, like adults jammed into middle seats while my toddlers lounge like kings in the captain’s chairs.

Recently though, a fellow mom (who also happens to be a Car Seat Safety Technician) shared a car seat installation rule I’d never heard before: The LATCH system in most vehicles is only built to accommodate a load of 65 pounds.

Sure, no problem, I thought. My oldest is nowhere near 65 pounds. But, she pointed out that 65-pound limit includes the weight of the child restraint, a.k.a. car seat. Do you realize how heavy car seats are these days? In order to use the LATCH system, the sum of the child’s weight and the weight of the car seat must be no more than 65 pounds. Since most car seats weigh upwards of 20 pounds now, many manufacturers recommend that you stop using the LATCH system when a child reaches 40 pounds. I had no idea!

Now my son’s car seat is secured with the seat strap. When he’s done with the five-point harness and transitions to using the seat strap himself, we can return to using the LATCH system. At that point, the straps are made to absorb his impact in the event of a crash, and the LATCH system would then only be used to keep the seat from catapulting through the car. For a list of LATCH weight limits by manufacturer, refer to your car’s manufacturer.

A version of this story was originally published on Sept. 19. 2019. It has been updated by Motherly editors.