It’s not just an urban legend—you really can break your penis. But since there aren’t any actual bones in your boner, it’s not quite the same injury as, say, fracturing your arm.

The condition is known as a penile fracture, and it occurs when your erect penis sustains some kind of force.

First, a refresher on what makes up your erection: Your penis consists of three cylindrical tubes. The two larger tubes are called the corporeal bodies—think of them as “balloons”—that fill up with blood when you become hard.

The “skin” of these balloons is the tunica albuginea, a tissue that expands both length- and width-wise during an erection, says Jacob Rajfer, M.D., professor of urology at the David Geffen School of Medicine at UCLA.

The third, smaller tube—located on the underside of your penis—is your urethra, from which you urinate.

When you get aroused, blood rushes into those two larger tubes, and the pressure grows. That makes your penis rigid and hard to bend. So if it experiences some kind of force—like if you accidentally hit your girlfriend’s perineum during sex while thrusting, or she moves it too much when grinding on top—it can lead to pressure overload.

“The surrounding tissue that’s holding the pressure inside can’t withstand it anymore,” says Dr. Rajfer. “And that’s when the rupture occurs.”

Penile fractures happen only when you have an erection. When you’re soft, the pressure inside your penis is low, so it’s more able to bend and withstand unexpected forces.

What Are the Symptoms of Penile Fracture?

If you’ve fractured your penis, you’ll usually know immediately. One of the most telling symptoms is a cracking or popping sound—that’s actually the tissue tearing.

You’ll also probably lose your erection right away, similar to what happens if you stick a pin in a blown-up balloon. Then comes swelling, black-and-blue bruising, and, of course, pain. Lots and lots of pain.

If the injury also affects your urethra, you might notice blood when you urinate. This means your urethra has ripped, says Dr. Rajfer.

What Should You Do If You Fracture Your Penis?

Any of those symptoms during sex should tell you that something’s not quite right below your belt. And while it might be embarrassing to hit the emergency room with your penis problem, that’s exactly what you need to do.

The doctors at the ER can confirm your penile fracture through a clinical exam and also by tests like an urethrogram, an MRI scan, or a cavernosogram, which is an X-ray of the penis.

Occasionally, you may need a cystoscopy—a procedure in which a hollow tube equipped with a lens can look directly inside your urethra—to determine whether it’s actually torn.

You’ll usually require surgery to repair the tear in your penile tissue. And it’s important that you go under the knife within 3 days of the injury. This isn’t a wait-and-see condition—if you put it off too long, you can raise your risk of complications down the line.

“It becomes much more difficult to repair it, and scarring can start to form,” says Dr. Rajfer.

This scarring can lead to a curve in your penis when you get an erection, or you might find yourself unable to even get hard in the first place. That’s because the tissue that holds the blood in with an erection is damaged, resulting in erectile dysfunction (ED).

If you see a doc in a timely fashion and get the surgery within 72 hours of the injury, your prognosis is pretty good, says Dr. Rajfer. You should even be able to have sex again about 4 to 6 weeks post-op.

How to Avoid Breaking Your Penis

The good news: Penile fracture is a relatively uncommon condition, so you don’t need to brace yourself for that pop each time you get busy in bed.

But there are some sex positions that seem to be a bit more risky for your penis. In a Brazilian study, half of all penile fractures that occurred during sex were from the woman-on-top position. In comparison, only 21 percent of cases stemmed from missionary.

That might be because when she’s on top, she controls the movement, and her entire body weight is landing on your erect penis. Plus, if there’s a slip, she might not be able to interrupt it in time, says study author Leonardo Reis, M.D., Ph.D.

Reduce your risk by making sure you’re fully erect before penetrating her. If you’re not, your penis may be more likely to torque or twist, which could raise the risk of penile fracture, says Dr. Rajfer.