Sales at U.S. retailers surged in July to the highest level of 2017, aided by strong demand for new autos and Amazon’s Prime Day shopping specials.

Sales at retailers nationwide jumped 0.6% last month, the government said Tuesday. Economists polled by MarketWatch had forecast a 0.4% increase.

A mysterious decline in spending at the end of the second quarter, meanwhile, vanished after fresh government revisions based on newly incorporated sales data.

Retail sales actually rose 0.3% in June instead of falling 0.2% and sales in May were flat. The retail report can be quite volatile and subject to large revisions.

The latest report on retail sales shows households still had plenty of buying power as the third quarter got under way in July. Consumer spending is by far the largest source of U.S. economic activity.

Steady hiring, the lowest unemployment rate in 16 years and gently rising incomes have all buoyed spending in 2017, keeping the economy on a modest growth path more than eight years after an expansion took hold.

“The inherent volatility in the monthly retail sales reports notwithstanding, consumers will remain the key driver of growth in the U.S. economy,” said Richard Moody, chief economist of Regions Financial.

Sales in July were the highest since December. Americans increased spending last month on most goods except for clothes and gasoline.

Sales at electronic stores also fell slightly, but in all likelihood consumers merely shifted purchases to online retailers such as Amazon.

The giant online seller held its annual Prime Day last month offering cut-rate prices on thousands of goods. That helped boost sales of so-called nonstore retailers by 1.3% last month, the largest increase since December.

Sales also rose 1.2% at auto dealers, 1.2% at home and garden centers and even 1% at department stores that have been losing ground to internet rivals.

Excluding auto and gasoline, retail sales still rose a healthy 0.5% in July.

Retail sales have climbed 4.2% in the past 12 months, close to the five-year average.