Nothing’s more satisfying than an extra-long night of sleep, especially when you’ve been feeling a little sleep deprived. But a new study finds that sleeping more than 8 hours a night might do more harm than just causing social jet lag — it may increase your risk of stroke.

A new February 2015 study from The University of Warwick in the U.K., published in the journal Neurology, analyzed close to 10,000 British adults’ (42- to 81-years-old) self-reported sleeping times over 9.5 years. It turns out that sleeping too much could potentially be more dangerous than sleeping too little: Participants who reported sleeping over 8 hours each night had double the risk of stroke compared to those who slept between 6-8 hours each night. Those who slept for less than 6 hours or more than 8 hours were more likely to be older, women and less active.

READ MORE: 10 Reasons to Get 8 Hours of Sleep Tonight

The study also found that those whose sleep durations changed (specifically, increased) over the years had an even higher risk than those who maintained an average night’s sleep. These findings held true after adjusting for age and sex and combining data from 11 other related studies.

However, the part that researchers couldn’t determine from the data on hand was the why getting more sleep correlates with a higher risk of stroke. But the researchers say more studies need to be done to determine what could be behind the troubling association. One potential factor is that some of those who sleep longer do so because of an underlying health issue, which is what actually causes the higher risk.

According to recently updated guidelines from the National Sleep Foundation, adults between 18- to 64-years-old should be getting 7 to 9 hours of sleep each night. Many studies have shown not sleeping enough can have dire health consequences, too, so focus on hitting that sweet spot of 7 to 8!

READ MORE: She Had a Stroke at 27—And Her Doctors Didn’t Notice