WASHINGTON (AP) — U.S. businesses sharply cut the number of jobs they advertised in December for the second straight month, an unusual sign of weakness in an otherwise healthy job market.

The number of available positions dropped 5.4% to 6.4 million, a historically solid number, the Labor Department said Tuesday. There are still more open jobs than there are unemployed people, an unusual situation that has persisted for nearly two years. Before that, the ranks of those out of work exceeded the number of open jobs.

Still, the total of available jobs has fallen by more than 1 million in the past year, the biggest annual drop since the Great Recession. Most of that decline has occurred in just the past two months. Job openings are now at the their lowest level in two years. The decline comes after job openings had hit the highest level on records dating back to December 2000.

Nearly all other measures of the labor market remain healthy: The unemployment rate is 3.6%, nearly a half-century low, and employers added 225,000 jobs last month, a solid increase.

“The trend in job growth has remained strong through January … but the recent decline in job openings signals that job growth could slow at some point,” said Daniel Silver, an economist at JPMorgan Chase.

Over the past two months, openings have fallen across all large industries covered by Tuesday’s report, known as the Job Openings and Labor Turnover survey, or JOLTS. Some of the biggest declines were in construction, manufacturing, financial services, and retail.

Other data in the report suggested hiring and the job market remains solid. Total hiring rose 1.4% to 5.9 million in December. The JOLTS tracks gross hiring, while the monthly jobs report counts net job gains. The Labor Department said last month that employers added a net total of 147,000 jobs in December.

Layoffs also rose in December to nearly 1.9 million, the highest in more than two years. But that number is historically volatile and may not signify a shift in trends. As a percentage of the workforce, job cuts remain low. And weekly figures on unemployment claims also point to a low level of layoffs.

The number of Americans quitting their jobs declined moderately, but remains at a healthy level. More frequent job departures are typically a sign of job market health, because most workers leave their jobs for a better or higher-paying position.