American consumers tightened their purse strings unexpectedly last month, breaking a seven-month winning streak, government data showed Wednesday.

Shoppers took home fewer autos and spent less on gasoline, groceries and building supplies while buying less online as well, according to the Commerce Department.

The September slump meant momentum waned at the end of the third quarter and could be a worrying development for the world’s largest economy.

The American consumer is almost single-handedly sustaining the US expansion as the economy in the rest of the world slows and President Donald Trump’s trade wars eat into US exports, business investment, manufacturing and agriculture.

The September dip in sales looked bigger after August’s numbers were revised upward, however.

Compared to August, total retail sales fell 0.3 percent to $525.6 billion, the first decline since February. Economists had instead expected a 0.3 percent increase, as shoppers moved to buy at lower prices ahead of looming tariff increases on Chinese goods.

Compared to September of last year, sales were up 4.1 percent.

Sales of autos and parts slumped 0.9 percent while gasoline stations were down 0.7 percent.

But, even when these volatile categories are excluded, the picture was not much brighter, with sales flat for the month.

Ian Shepherdson of Pantheon Macroeconomics said other data showed September had been stronger than it appeared, meaning the latest numbers were likely to be revised upward.

Upward revisions occur more frequently than downward ones for retail sales, he wrote in a client note, “and today’s numbers look like prime candidates to be moved higher.”

However, sales growth in the fourth quarter was likely to continuing slowing, falling back in line with slower growth in after-tax income, he said.