The market closed 30 minutes later than usual at 5:30 pm (2030 GMT) to compensate for a 90-minute communications failure at midsession.
"With the expectations of a successful swap the MerVal continues advancing and today it could have reached 1,600 points if it weren't for sales of Group Financiero Galicia and Banco Frances which traded in big volumes at low prices," said Oscar Campos, trader with Intervalores brokerage.
In a bid to end three years of default, the government is offering private creditors new debt in exchange for bad debt at a loss of up to 70 percent. Many Wall Street analysts forecast some 70 percent of bondholders will take the offer.
Steelmaker Acindar gained 4.5 percent to 6.97 pesos after it reported a 9 percent drop in net profit last year but said revenue rose sharply.
Group Financiero Galicia dropped 0.37 percent to 2.69 pesos and Banco Frances slipped 0.41 percent to 7.25 pesos.
In the foreign exchange market, the peso backtracked from nine-month highs after the central bank intervened to reduce liquidity in dollars, traders said.
The currency closed 0.34 percent lower at 2.91/2.915 per dollar.