Imperial Tobacco has said it will take a one-off loss of £140m ($280m) due to accountancy adjustments relating to its January takeover of rival Altadis.
Imperial is the world's fourth-largest tobacco company
The UK group, the world's fourth biggest cigarette-maker, bought Franco-Spanish Altadis for 12.6bn euros ($19.9bn; £9.9bn) in January.
Imperial said its trading conditions remained in line with expectations.
Cigarette brands owned by the Bristol-based company include Lambert & Butler, West and Gauloises.
"The adjustments will have no effect on the underlying business performance or cash flows of the group," it said in a statement.
Shares in the firm were down 1% in Wednesday trading.