The monthly Architecture Billings Index (ABI) came in at a score of 55.9 in December, up 5.3 points from November’s 50.6, the American Institute of Architects announced today.

The ABI is a leading economic indicator of construction activity in the U.S., and reflects a nine- to 12-month lead time between architecture billings and construction spending nationally, and regionally, as well as by project type. A score above 50, like this month, represents an increase in billings from the previous month, while a score under 50 represents a contraction.

The significant growth in billings does not come as a surprise, as the new project inquiries index, the most reliable indicator of future billings, soared to a score of 59.5 in November—4.1 points higher than a month prior.