Home sales were down again in December, the 11th straight month of decline, according to the latest report from the National Association of Realtors (NAR). And while home prices continue to rise, it’s the lack of inventory that has many investors and observers concerned.

According to the NAR report, the total housing inventory at the end of December stood below 1 million at 970,000, down 13.4% from November with a 2.9-month supply at the current sales pace. That number was down from 3.3 months of inventory in November.

“December was another difficult month for buyers, who continue to face limited inventory and high mortgage rates,” NAR Chief Economist Lawrence Yun said. But Jack Macdowell Jr., co-founder and chief investment officer of the Palisades Group, told Benzinga that the bottom line is “we need more product on the market.”