So let’s say you decided to place your home or a few rooms inside it among the million-plus listings that the rental site Airbnb now claims to have.

And let’s also say that you’re the rule-abiding sort and find the part of the company’s website where it encourages you to check with your homeowners or renter’s insurance company to make sure you have proper liability coverage for guests.

What would happen if you did so? If you’re Julie Pfeffer, who rents two rooms in her 200-year-old home in Hockessin, Del., and your insurer is State Farm, it would tell you that your policy was going to be canceled in 30 days. At which point, you would be in a real pickle.

Airbnb now provides backup liability protection for people who put United States listings on its site. It kicks in when and if your own insurance company denies the claim, and many would, given that they don’t like covering commercial activity in people’s homes. This secondary coverage is all well and good, but most homeowners need (or at least want) primary coverage in the first place. Their mortgage company probably requires it, or they worry about placing too much faith in the free liability coverage provided by a start-up like Airbnb. And if insurers won’t sell any coverage to homeowners if they have a part-time home rental operation going on, it will be trouble for everyone involved.