Receiving generosity can evoke feelings of gratitude, which can in turn promote prosocial behaviour. However, past research on the link between gratitude and generosity has been limited to low-stakes economic games in labs. Do feelings of gratitude predict more prosocial spending in real-world settings? We took advantage of a one-of-a-kind study, where 200 individuals across 7 countries were unexpectedly given $10,000 USD to spend as they liked within 3 months. We asked participants how they felt on receiving the money, and coded the responses. Shock or joy were most commonly expressed, but around 15% of participants spontaneously reported gratitude as well. We then tracked how participants spent the money. We found that those who spontaneously reported gratitude spent more money on others compared to those who didn't. This suggests that generosity can become 'infectious' through the medium of gratitude, which enhances generous spending decisions in real world, high-stakes situations.