diff --git a/has-project/has-client/src/main/java/org/apache/kerby/has/client/HasLoginModule.java b/has-project/has-client/src/main/java/org/apache/kerby/has/client/HasLoginModule.java
index 8debda5..e222020 100644
--- a/has-project/has-client/src/main/java/org/apache/kerby/has/client/HasLoginModule.java
+++ b/has-project/has-client/src/main/java/org/apache/kerby/has/client/HasLoginModule.java
@@ -78,7 +78,7 @@
     private PrincipalName principal = null;
     private KerberosPrincipal kerbClientPrinc = null;
     private KerberosTicket kerbTicket = null;
-    private StringBuffer krb5PrincName = null;
+    private StringBuilder krb5PrincName = null;
     private boolean unboundServer = false;
 
     /**
@@ -157,10 +157,10 @@
             }
             String principalProperty = System.getProperty("sun.security.krb5.principal");
             if (principalProperty != null) {
-                krb5PrincName = new StringBuffer(principalProperty);
+                krb5PrincName = new StringBuilder(principalProperty);
             } else {
                 if (princName != null) {
-                    krb5PrincName = new StringBuffer(princName);
+                    krb5PrincName = new StringBuilder(princName);
                 }
             }