diff --git a/audit/api/model.go b/audit/api/model.go
index 4e80019..e3f9e69 100644
--- a/audit/api/model.go
+++ b/audit/api/model.go
@@ -617,6 +617,10 @@ func AuditAttributesFromAuthorizationHeader(request *Request) (
 	var delegationInfo []*auditV1.ServiceAccountDelegationInfo = nil
 
 	authorizationHeaders := request.Header["Authorization"]
+	if len(authorizationHeaders) == 0 {
+		// fallback for grpc where headers/metadata keys are lowercase
+		authorizationHeaders = request.Header["authorization"]
+	}
 	authorizationHeader := strings.Join(authorizationHeaders, ",")
 	trimmedAuthorizationHeader := strings.TrimSpace(authorizationHeader)
 	if len(trimmedAuthorizationHeader) > 0 {