U.S. Customs and Border Protection agents recently seized more than 12,000 pounds of marijuana that was hidden inside a load of sheet rock on a flatbed truck, the agency announced.

The incident occurred at 3 a.m. Dec. 23 at the Border Patrol’s Falfurrias checkpoint. The town of Falfurrias lies about 75 miles north of the border town of McAllen, TX.

A Border Patrol agent conducted an immigration check on a driver after his white 1999 Freightliner tractor-trailer entered the checkpoint. A canine team also took a sniff around the rig, and one of the dogs alerted agents to something on the trailer.

The driver was directed to the secondary inspection area for a closer inspection of the trailer, a release from the patrol said.

When agents searched the trailer, they found 299 bundles of marijuana weighing 12,139 pounds – a load valued at $9.7 million.

“This drug seizure illustrates the continued threat posed by smugglers attempting to bring illegal drugs into our country,” McAllen Sector Chief Patrol Agent Ramon Ortega said in a statement.

The driver, a U.S. citizen from Roma, TX, was arrested and transferred, along with his rig and the drugs, to the Drug Enforcement Administration office in Corpus Christi, TX.