Speaking with the German newspaper Finanz und Wirtschaft this month, Pierre Lassonde, co-founder and chairman of mining royalty company Franco-Nevada, said he’s not sure how the world will be able to keep up the pace of discovery of gold deposits that it has enjoyed over the last century.

“What the industry has not done anywhere near enough is to put money back into exploration,” Lassonde told the paper. “They have not put anywhere near enough money into research and development, particularly for new technologies with respect to exploration and processing.”

In the long term, he warns, there could be a supply-demand imbalance and an increase in the price of gold around the world. The issue, in part, is that mining has slowed down due to increased costs and decreased discovery of new mining locations. The Trump administration has also been blamed for the recent surge in gold prices.

Lassonde, as well as Frank Holmes, who wrote an article about the issue for U.S. Global Investors, suggests that investors should start including gold in their portfolio if they haven’t already. Holmes recommends keeping between 5 and 10 percent of your portfolio in gold, and adding gold stocks to the mix, particularly those that are typically overlooked and undervalued.