Constellation Brands just served up a major buzzkill.

Shares of the Corona brewer — which blew minds on Wall Street in 2017 with a $4 billion cannabis investment — plunged more than 12 percent on Wednesday after it warned of weak demand for its cheap wine labels and admitted it overpaid on its big pot deal.

While its premium labels like Kim Crawford and Prisoner are getting gulped up greedily, drinkers aren’t downing low-price wines like they used to, Constellation execs admitted as they reported fiscal third-quarter results.

Accordingly, the company slashed its outlook for sales of downmarket brands like Robert Mondavi and Black Box — the latter of which gets served straight out of cardboard boxes.

Now, Constellation is predicting wine sales will drop in the low-single digits this year versus a previous projection of 2 percent to 4 percent sales growth.

“We’re disappointed with the performance of our wine and spirits business as we’re facing challenges with the low end of the portfolio,” Constellation president Bill Newlands said on a call with analysts.

As a result, Constellation said it is exploring “strategic alternatives” to sell its wines that retail below $11 a bottle. Those include Arbor Mist, Cooks, and Woodbridge.

“We believe it’s urgent that Constellation address its low­-end wine business,” Wells Fargo analyst Bonnie Herzog said in a note Wednesday.

That’s not all Constellation needs to fix.

Last year, the brewer of Negra Modelo and Svedka vodka stoked broad interest in the budding cannabis business with its $4 billion investment in Canadian pot grower Canopy Growth.

But since closing the debt-financed transaction in November, Constellation has written down the value of its stake by $164 million and said it expects interest expenses will hit full-year earnings by 25 cents a share.

While Constellation was lauded for being one of the first major players to invest in cannabis, marijuana remains illegal under federal law in the US.

Constellation shares closed at $150.94.