This study investigates the behavior of investors in sustainable investment funds in the United States over the past few years. Previous research has suggested that these investors are less sensitive to financial performance compared to investors in conventional funds. However, the growth of both demand and supply for sustainable investment products in recent years may challenge this assumption. Using data on 2,103 U.S. active equity mutual funds from August 2018 to December 2021, we provide evidence that investor sensitivity to past performance of sustainable funds has increased as sustainable investing becomes mainstream. In contrast to prior research based on earlier periods, we show that investors in sustainable funds are more sensitive to past performance than investors in conventional funds. We show that this strong sensitivity is driven by poor performance, indicating that sustainable investors are more likely to sell losing investments than their conventional peers. Our results also reveal that the flow-performance relationship is not convex for U.S. sustainable funds over the sample period, meaning that investors in these funds do not exhibit the typical behavior of chasing winners more intensely than selling losers. Furthermore, we find evidence of a “smart money” effect for sustainable funds, in which past money flows enhance fund performance. This result suggest that sustainable investors are financially smart in their investment decisions. Overall, our findings indicate that financial performance and sustainability are now complementary rather than substitutes for investors, contrary to traditional beliefs, and should therefore be considered jointly by fund managers when selecting assets.