Technology researchers from McAfee Advanced Threat Research (ATR) have managed to trick the Mobileye technologies used in Tesla’s first-generation Autopilot system to misread 35 mph speed limit signs as 85 mph signs.

Mobileye’s advanced camera system is used by more than 40 million vehicles worldwide, including select Tesla models, and researchers set out to discover how just a small modification made to a speed limit sign can trick the system.

To do so, ATR used a small piece of black tape to modify a 35 mph speed limit sign so that to the human eye, it is still discernible as 35 but to Mobileye’s camera system looks like an 85. If a car with speed limit recognition and cruise control enabled came across a 35 mph sign modified this way, it could automatically accelerate up to 85 mph, as demonstrated with a Tesla Model S.

Also Watch: This Is What Tesla’s Autopilot Sees On The Road

Before you think about modifying 35 speed limit signs in a bid to fool cars with a Mobileye system, McAfee says it alerted Tesla and Mobileye to the issue 90 days before publicizing the speed limit trick.

“McAfee Advanced Threat Research follows a responsible disclosure policy, as stated on our website. As such, we disclosed the findings below to both Tesla and MobilEye 90 days prior to public disclosure,” the company said. “McAfee disclosed the findings to Tesla on September 27th, 2019 and MobilEye on October 3rd, 2019. Both vendors indicated interest and were grateful for the research but have not expressed any current plans to address the issue on the existing platform. MobilEye did indicate that the more recent version(s) of the camera system address these use cases.”