The Barcelona player and his father were found guilty by a Catalan court last year of three counts of tax fraud to the tune of 4.1 million euros (3.63 million pounds) over income earned from image rights.
The father also had his 15-month sentence exchanged for a fine of 180,000 euros, the court said.
Neither Messi or his father would have served time in jail following the original ruling as defendants without a previous conviction are permitted to serve any sentence of under two years on probation.
(Reporting by Emma Pinedo; Writing by Paul Day)
