ROME--Italy's long recession is technically over, as gross domestic product stopped shrinking in the third quarter, according to new revised data from national statistics institute Istat.

Italian real GDP was unchanged from the previous three months, and down 1.8% from the third quarter of 2012, Istat reported Tuesday.

The new data say Italy's longest post-war recession formally ended over the summer after eight consecutive quarters. It also puts the government on track to meet or even beat its forecast that GDP will have declined by 1.8% over all of 2013.

The improvement was led by an inventory buildup, which is a sign of growing confidence among companies that they will be able to sell their output, although domestic buyers may not step up to the plate for a while.

"We are exporting a lot and bullish on that front, but in terms of domestic demand, I really don't see any signs of a recovery in the construction sector until 2015, " Mauro Vandini, chief executive of tile-maker Marazzi SpA, a unit of U.S.-based Mohawk Industries, said in an interview. "That's kind of a snapshot of the economy as a whole."

Measured in terms of expenditures, Italian GDP was lifted by inventories even as fixed business investments fell by 0.6% from the previous quarter and household spending declined by 0.2%, according to Istat's data.

"It's too early to say that the recession is finished," an Istat official said.

Italy's farming sector shrank by 1.6% in real terms during the three months through September, while services and construction remained unchanged. The industrial sector, where the inventory effect is largest, posted a 0.2% gain, Istat said.

Write to Christopher Emsden at chris.emsden@wsj.com