We find that the tail risk of a firm's stock returns is positively affected by the tail risk of other firms held by the same common institutional blockholder (CIB). The CIB peer effect on tail risk increases (decreases) after exogenous initiations (terminations) of peer connections via CIB ownership, consistent with a causal interpretation. Our findings support the disclosure herding hypothesis, which predicts that firms release bad news after other firms’ bad news announcements. In addition, commonality in the real investment decisions of a firm and its CIB peers, along with the common trading pressure of these firms, contribute to the positive relationship between firms’ tail risk, highlighting the multifaceted roles of institutional investors in the contagion of firms’ tail risk. Finally, the CIB peer effect on tail risk is stronger when the CEO is more risk averse, CIBs hold more shares, or CIBs are pressure-sensitive (i.e., banks and insurance companies).