DETROIT -- Before Justin Bieber performed Sunday night in Detroit at Joe Louis Arena, border guards searched one of his tour buses and discovered marijuana.

Kenneth Hammond, a spokesman for U.S. Customs in Detroit, told the Detroit Free Press that the singer was not on the bus at the time.

Hammond said the bus was entering the U.S. from Windsor, Ont., via the Ambassador Bridge when a police dog alerted guards to the presence of drugs.

He told the newspaper that customs officers seized a small amount of marijuana intended for personal use and drug paraphernalia.

Hammond said the bus driver was issued a civil penalty and the bus and its passengers were released.

Bieber is next scheduled to perform two shows in Newark, N.J., on Tuesday and Wednesday nights as part of his Believe Tour.