Preliminary official figures show that German retail sales jumped by a surprising 3.1% in August. Analysts had forecast an increase of just 0.5%.
In July, sales had fallen by 1% in Europe's biggest economy, the Destatis statistics agency said, revising an initial estimate of a 1.5% drop.
German consumers are traditionally thrifty, and consumption has in past months been one of the economy's weak links despite falling unemployment and significant increases in wages.
The volatile index is calculated from information provided by seven German states.
