Just when you thought you’d heard of all the things that can go wrong with your penis, Jimmy Kimmel reveals a new one.

The comedian’s urethra once closed up, he for some reason blurted out at a SXSW panel last week. He needed two surgeries to fix it, calling it a “horrible, horrible process.”

Lee Zhao, M.D., a professor of urology at NYU Langone Medical Center, confirms that your urethra—the tube that carries urine and semen to the end of your penis—really can just jam up.

It’s called a urethral stricture. Scar tissue builds up in the tube, Dr. Lee says, narrowing the opening. That makes it hard to pee: The stream becomes slow and it may hurt, he says. Eventually, the tube can close completely.

But what causes the scar tissue? Trauma to your perineum is one possible culprit, Dr. Lee says. (It’s your worst nightmare and the subject of a million YouTube videos: Falling and landing with a rail in your crotch.) A previous surgery on your penis or an infection could also be the cause. But in most cases, Dr. Lee says, doctors aren’t sure.

No one knows how many guys this happens to, but Dr. Lee estimates it’s less than 1 percent of men.

There are a couple treatment options: Doctors may go into your urethra with a scope and either stretch the tube with a plastic rod, or snip a tiny slit into the scar tissue to make the opening bigger.

The other route is a surgery called a urethroplasty, which is used for more advanced cases, Dr. Lee says. In that procedure, the surgeon removes the scarred part of the urethra completely and then puts the two ends of the tube back together, sometimes with tissue from your mouth.

Fun stuff, right?

Unfortunately, because doctors don’t know what causes the scarring in most cases, Dr. Lee says there’s not much you can do to prevent it. (Other than not doing rail tricks on skateboards.)

But if you do start experiencing symptoms like painful urination, weak flow, or recurring UTIs, see your doc or a urologist right away.