diff --git a/pattern-singleton/src/main/java/org/panda/singleton/Singleton.java b/pattern-singleton/src/main/java/org/panda/singleton/Singleton.java
index d557ec9..0d667db 100644
--- a/pattern-singleton/src/main/java/org/panda/singleton/Singleton.java
+++ b/pattern-singleton/src/main/java/org/panda/singleton/Singleton.java
@@ -7,7 +7,7 @@ package org.panda.singleton;
  */
 public class Singleton {
 
-    private static Singleton singleton = new Singleton();
+    private static final Singleton singleton = new Singleton();
 
     private Singleton(){