diff --git a/kms.go b/kms.go
index 01e6d125..9f2a46c4 100644
--- a/kms.go
+++ b/kms.go
@@ -24,7 +24,7 @@ const (
 )
 
 func (c *Client) kmsAuth(url string) error {
-	if c.options.KerberosServicePrincipleName == "" {
+	if c.options.KerberosClient == nil {
 		url += ("&user.name=" + c.options.User)
 	}