Anyone planning to accentuate their new Apple Watch with a nice wrist tattoo, may want to rethink that decision. Early adopters of the Apple Watch are reporting on Reddit, Twitter, and other social media that tattoos disrupt some of the watch’s key functions.

According to Reuters, tattoos seem to interfere with the sensors on the the underside of the watch. Users on Reddit discovered that the device’s locking mechanism, which is supposed to disengage when the watch detects it is being worn, failed to work on tattooed skin. Reuters additionally found that tattoos may disrupt notifications as well.

“This Reuters reporter, who has a black tattoo on his left arm, also found that the watch locks on tattooed skin and does not deliver the soft pings that alert a user to incoming messages,” wrote Matt Siegel.

The Verge reports that the watch also gives inaccurate heart rate results when placed over tattoos, a problem shared by other fitness bands. Tests conducted by iMore demonstrated that dark, solid colors seemed to give the sensor the most trouble, while lighter colored tattoos led to heart rate stats a little less inaccurate.

An Apple support article, found by Reuters, describes how the watch uses green LED lights paired with light-sensitive photodiodes to detect the amount of blood flowing through the wrist and calculate the frequency of heart beats. Consequently, it is not surprising that a tattoo can interfere with this process.

The Apple Watch’s heart rate tattoo problem has an easy fix: a compatible Bluetooth heart rate chest strap. But the failure to even recognize that the watch is on a wrist is another matter entirely. And no fix for that exists at the moment.

Potential Apple Watch purchasers with any kind of ink or decoration on their arms or wrists would do well to try one out at the Apple Store before forking over their hard earned cash for a watch that might not even work properly.