The rules about machine guns and machine gun parts are troubling for many Americans. While it’s technically legal for most of us to own them, there are piles of regulations that go into buying, making, or owning fully-automatic firearms. In fact, there are so many that most folks who might like to own such weapons and have the financial means to own them simply don’t bother with doing so.

After all, they’re not exactly something you can slip on down to your local gun store and pick up in an afternoon.

However, just possessing them can be a problem, such as the problem one Pennsylvania man found.

Donald Leroy Miller used his skill assembling guns to earn money after losing his job, his attorney said, but making machine guns for his clients cost him his freedom.

U.S. District Judge Edward G. Smith on Monday sentenced Miller, 48, of Northampton to two years in prison followed by three years of supervised release. Smith also ordered Miller to pay a $700 fine.

Miller pleaded guilty in May to possession of machine guns, possession of guns not registered to him in the National Firearms Registration and Transfer record and possession of firearms as a convicted felon.

According to court documents, Miller possessed a DPMS Panther Arms A-15 .223-caliber frame and a Battle Arms Development .223-caliber rifle, both capable of firing more than one shot automatically with a single pull of the trigger. Under federal firearms law, a frame of a gun — also called the receiver — is considered a firearm even if it lacks all of the parts necessary to fire.

So Miller was basically just building AR-15s, but the receivers in question were set up for full-auto, meaning he was in possession of a Class III firearm without the proper licensing.

Of course, this is a prime example of something any of us could fall into if we’re not careful.

While Miller was a convicted felon–he had a non-violent drug arrest 30 years ago–there’s no evidence he had any intentions to commit any violent action. That would be why he got the lenient sentence. Take that away and what you get is a man who was building rifles for people to make a little extra money, only to not realize that he had a full-auto receiver.

Ignorance, however, is not considered a valid defense.

Then again, it’s likely some would debate whether Miller was actually that ignorant or not. Frankly, I don’t care. There’s no evidence I see to suggest he was intending anything malicious. In fact, I know some folks who have put together a rifle for friends here and there themselves for some extra money. One thing they all do, though, is make sure they recognize a full-auto receiver when they see one. The last thing any of them want is to end up in prison over an oversight.

Miller should have, at least, done that. If he had, it’s unlikely that anyone would have looked at his side work building guns. Unfortunately, he didn’t and they did.