One bedroom move could put your manhood in jeopardy: Brazilian research finds roughly half of sex-related penile fractures happen during woman-on-top sex. 

Doggystyle mishaps were a distant second, at 28 percent. (If you’re wondering about those non-sex-related fractures, breaking your penis while masturbating is surprisingly common, according to the study.)

Related: The Men’s Health Guide to Erectile Dysfunction—For Guys Who Are Serious About Fixing Their Problems In the Sack 

What is a penis fracture? There are sponge-like tubes of tissue in your rod that, when filled with blood, become as rigid as uncooked spaghetti, explains Tobias Köhler, M.D., a urologist at Southern Illinois University.

If you put too much force on your erect penis, those tubes don’t bend—they “break.” That leads to blood blockages, lots of pain and swelling, and an emergency trip to the hospital, says a related study from Ohio State University. 

If a doctor doesn’t take care of the fracture ASAP, you could be permanently deformed and lose function, the study authors say. 

The problem with woman-on-top sex: She’s in control of the vigor and angle of your penis’s path into and out of her vagina, which is an area surrounded by several hard, bony surfaces.

Related: The 10 Worst Penis Injuries

Fractures happen when your penis slips out of her vagina and smashes into one of those unforgiving surfaces, or if she sits down on your manhood at a funny angle, the Brazilian study authors say. 

How can you avoid fracture-related calamity? Pretty much every other position besides her-on-top gives you control over the angle and depth of penetration, which limits your risks, the study suggests. 

Also, take it a little easy in the sack. Your penis is more likely to slip out of her during vigorous sex, Dr. Köhler says.

Related: 4 Dangerous Sex Positions

Staying calm and in control helps you avoid the poor angles and unfortunate penis-to-pelvis collisions that lead to fractures, he adds.