I have a bag that very slightly exceeds the Air France carry-on mandate. I don't fly them often, so it's not worth getting a new bag to meet that standard.

I have one checked bag included in my fare, but prefer not to check my bag if I don't have to. If I chance it and at the gate they determine it is not acceptable for carry on, will they charge me a fee to gate check it? Or because I have one checked bag allowed that I haven't used yet, would it just be gate checked at no charge?

I know it used to be pretty common to simply have a bag gate-checked at no cost, but now that many airlines are trying to charge fees for anything they can I'd like to have an idea going in. And I haven't been able to find anything useful searching Air France's website or other threads here on Flyertalk.