diff --git a/x-pack/plugin/security/src/main/java/org/elasticsearch/xpack/security/authc/ldap/ActiveDirectorySIDUtil.java b/x-pack/plugin/security/src/main/java/org/elasticsearch/xpack/security/authc/ldap/ActiveDirectorySIDUtil.java
index 8cb6e128d17e5..701215dcfe703 100644
--- a/x-pack/plugin/security/src/main/java/org/elasticsearch/xpack/security/authc/ldap/ActiveDirectorySIDUtil.java
+++ b/x-pack/plugin/security/src/main/java/org/elasticsearch/xpack/security/authc/ldap/ActiveDirectorySIDUtil.java
@@ -38,7 +38,7 @@ static String convertToString( byte[] bytes )
         }
 
         char[] hex = Hex.encodeHex( bytes );
-        StringBuffer sb = new StringBuffer();
+        StringBuilder sb = new StringBuilder();
 
         // start with 'S'
         sb.append( 'S' );
@@ -65,7 +65,7 @@ static String convertToString( byte[] bytes )
         // sub-authorities, little-endian
         for ( int i = 0; i < count; i++ )
         {
-            StringBuffer rid = new StringBuffer();
+            StringBuilder rid = new StringBuilder();
 
             for ( int k = 3; k >= 0; k-- )
             {