As interest rate-growth differentials (r-g) have turned negative in many countries, now could be the time for governments to pursue fiscal expansions. However, the downside risks of such policies should not be disregarded. Using a large sample of economies, this column finds that high and increasing public debts, especially when denominated in foreign currencies, can lead to more volatile r-g dynamics. In particular, this is associated with higher probabilities of r-g reversals, tail risks, and an increased exposure to domestic and global shocks. Policymakers should take note of these risks when designing future fiscal expansions.