Bayer stock fell more than 10% on Monday, representing a loss of more than $10 billion in market cap, on the first day of trading after a California jury found that the German company owed $289.2 million to a man who claims to have gotten cancer from exposure to Roundup weed killer.

The bottom line: Bayer might have taken on a bigger liability than it realized in buying Roundup maker Monsanto, via a $64 billion merger that closed this past June, as this could be just the first of thousands of similar lawsuits.