Customs and Border Protection agents discovered 254 pounds of fentanyl in a truck this weekend, NBC reports. It was the largest seizure of the synthetic opioid, which has caused countless overdose deaths, in U.S. history.

The bust took place Saturday when a tractor-trailer was stopped trying to enter the U.S. through a checkpoint in Nogales, Arizona. The driver, a 26-year-old man, was arrested and charged with possession and intent to distribute. No additional details about the driver were immediately made available.

A drug sniffing dog reportedly alerted authorities to the presence of the contraband, which was hidden in the floor compartment of a truck carrying cucumbers. Along with with the fentanyl, border patrol agents also found 395 pounds of methamphetamine. Customs and Border Protection estimated the value of the fentanyl at $3.5 million and the methamphetamine at $1.1 million.

The 254 pounds of fentanyl seized was over twice the size of the previous record-holding bust of 118 pounds, which Nebraska state troopers found in truck in 2017.

Fentanyl has played a large and deadly role in the ongoing opioid crisis. Last December, the National Center for Health Statistics released a report that found fentanyl had surpassed heroin as the drug most commonly cited in overdose death certificates.