Physical climate risks significantly influence banks' collateral practices. Drawing on comprehensive loan-level data from Sweden, we find that adverse weather events increase both the likelihood and the amount of collateral required for new loans. For existing loans, banks are less inclined to reappraise collateral following weather shocks; when reappraisals occur, collateral values are typically revised downward. Our analysis also highlights the mitigating role of geographic proximity between borrowers and lenders. Overall, our results indicate that while banks limit potential losses from physical climate risks by tightening collateral requirements, this practice may eventually exacerbate firms' financial constraints.