Afroman's learning a little ganja goes a long way in preventing you from crossing the Canadian border, where he got cited while trying to get back to the U.S. ... TMZ has learned.
Law enforcement sources tell us the Palmdale rapper and his crew were detained Tuesday by U.S. Border Patrol officers while they were attempting to get back on American soil at a port of entry crossing over the St. Lawrence River in upstate New York.
We're told they arrived at an inspection zone, where the feds found a ton of cash and some marijuana in their vehicle -- the bills totaled $10,000, but the bud was an insignificant personal amount.
Afroman tells TMZ ... he was on his way to a gig in NY when he was stopped at the border. He had given all his weed to his fans and housekeepers at his hotel but forgot about a bottle of cannabis pain lotion.
He says he was held for 5 hours at the border and fined $500 for the lotion -- and his DJ was also fined $500 for a small amount of cannabis gummies.
Law enforcement sources tell us the $10K was declared, and the weed was seized ... but nobody was arrested because it was such a small amount.
We reached out to U.S. Customs and Border Protection for comment. Spokesperson Mike Niezgoda would only say ... "As a matter of policy under the Privacy Act of 1974, we are unable to discuss a traveler's inspection."