Most corporate loans are priced at rounded spreads, e.g. spreads that are a multiple of 25 basis points. Using a sample of 16,598 loan tranches signed by US borrowers between January 1988 and December 2010, this study explores the determinants of such interest rate clustering in the corporate syndicated loan market. We postulate that lead arrangers round spreads upwards because of the uncertainty about the riskiness of the borrowers. Consistent with this negotiation hypothesis, we find that clustering increases with the degree of uncertainty, e.g. the degree of information asymmetry between the lead arranger and the borrower. In contrast, clustering is less likely when lead arrangers have acquired information about the borrower through prio...