Abstract Desecration of national symbols is a recurring societal phenomenon that can lead to highly defensive reactions from some citizens, especially on the part of those expressing a strong attachment to the nation. In this paper, we investigated the effects of blind and constructive patriotism when faced with an ingroup (vs. outgroup) national flag burning on ingroup bias, taking into consideration the mediating role of perceived threat. In two studies ( N = 252), the level of blind patriotism predicted stronger ingroup bias—due to more negative evaluation of visible minorities and/or more positive evaluation of the ingroup—when another ingroup member burnt an ingroup (vs. outgroup) flag. This effect was partly mediated by a greater threat to the group’s image perceived by blindly patriotic people when the ingroup (vs. outgroup) flag was burnt (Study 2). Study 2 also highlighted a main effect of the symbol: ingroup bias was stronger when the ingroup (vs. outgroup) flag was burnt. We discuss the implications of our findings with respect to the role played by modes of national attachment and the consequences of desecrating symbols.