Japan’s major automakers are facing growing uncertainty as the Iran war and efforts to strengthen the yen threaten to reverse some of the financial benefits that helped boost their latest earnings.

Toyota, Honda and Nissan all benefited from the historically weak Japanese currency in their most recent quarterly results. Toyota and Honda raised their full-year forecasts, while Nissan reported its first profit in roughly two years.

However, changing economic and geopolitical conditions could put pressure on future performance.

In early August, the U.S. Treasury and Japan’s Ministry of Finance jointly coordinated a rare intervention to support the yen after the currency weakened beyond 163 to the U.S. dollar, reaching levels not seen in about four decades.

A stronger yen could pose challenges for Japanese carmakers, which have traditionally benefited from a weaker currency. When the yen is weak, vehicles produced in Japan become more competitively priced overseas, while profits earned in foreign currencies are worth more when converted back into yen.

Analysts say sustained government efforts to strengthen the currency could therefore weigh on automakers’ earnings.

“If government intervention is to strengthen the yen, this would be negative for Japanese automakers,” Morningstar senior equity analyst Vincent Sun said.

The industry is also exposed to economic disruption stemming from the Iran war, which could affect energy prices, production costs, consumer demand and global supply chains.

Together, geopolitical uncertainty and the possibility of a stronger yen could create a more challenging environment for Toyota, Honda, Nissan and other Japanese manufacturers after a period in which favorable exchange rates helped support their financial results.