Economists had predicted prices producers charge for finished goods would be unchanged.
Core prices, which exclude food and energy -- rose 0.2 percent in the month. But energy prices alone dropped 1.4 percent while food prices separately rose 0.2 percent.
On an annual basis, finished goods price inflation settled at 1.9 percent for the month, down from 2.8 percent in March, 3.3 percent in February and 4.1 percent in January.
The downward streak began in September, when prices for finished goods rose 7 percent on an annual basis from August. The annual inflation rate has dropped each month since then. Last year, the annual rate peaked at 7.1 percent in May and July.