diff --git a/command/README.md b/command/README.md
index 476edc47af39..a3b863b78cbe 100644
--- a/command/README.md
+++ b/command/README.md
@@ -40,8 +40,8 @@ Here's the sample code with wizard and goblin. Let's start from the `Wizard` cla
 @Slf4j
 public class Wizard {
 
-  private final Deque<Command> undoStack = new LinkedList<>();
-  private final Deque<Command> redoStack = new LinkedList<>();
+  private final Deque<Runnable> undoStack = new LinkedList<>();
+  private final Deque<Runnable> redoStack = new LinkedList<>();
 
   public Wizard() {}