Japan’s current account surplus expanded 41.8 percent from a year earlier to 2.85 trillion yen ($18 billion) in May, the Finance Ministry said Monday.

According to Kyodo News, primary income came to a 4.21 trillion yen surplus, the largest since comparable data became available in 1985. It marked a 13 percent year-on-year increase.

The total surplus in the current account balance, one of the widest gauges of international trade, was the largest for the month of May.

Japan had a 1.11 trillion yen trade deficit as the weaker yen inflated the cost of imports for the resource-scarce nation, offsetting continued growth in exports.

Imports grew 9.3 percent to 9.24 trillion yen, while exports rose 12.1 percent to 8.13 trillion yen.