diff --git a/src/testcase/twitter/OAuthHeader.java b/src/testcase/twitter/OAuthHeader.java
index c06f144..1baacde 100644
--- a/src/testcase/twitter/OAuthHeader.java
+++ b/src/testcase/twitter/OAuthHeader.java
@@ -4,8 +4,9 @@
 import java.net.URLEncoder;
 import java.security.InvalidKeyException;
 import java.security.NoSuchAlgorithmException;
-import java.util.HashMap;
 import java.util.Map.Entry;
+import java.util.SortedMap;
+import java.util.TreeMap;
 
 import javax.crypto.Mac;
 import javax.crypto.spec.SecretKeySpec;
@@ -19,7 +20,7 @@
 	private String oauth_secret = "";
 	private String method = "POST";
 	private String url = "https://api.twitter.com/oauth/request_token";
-	private HashMap<String, String> params = new HashMap<String, String>();
+	private SortedMap<String, String> params = new TreeMap<String, String>();
 
 	public String getConsumer_key() {
 		return consumer_key;