diff --git a/Behavioral/Command/AddMessageDateCommand.php b/Behavioral/Command/AddMessageDateCommand.php
index 9543bda..11bb9af 100644
--- a/Behavioral/Command/AddMessageDateCommand.php
+++ b/Behavioral/Command/AddMessageDateCommand.php
@@ -6,7 +6,7 @@ namespace DesignPatterns\Behavioral\Command;
  * This concrete command tweaks receiver to add current date to messages
  * invoker just knows that it can call "execute".
  */
-class AddMessageDateCommand implements CommandInterface, UndoableCommandInterface
+class AddMessageDateCommand implements UndoableCommandInterface
 {
     /**
      * @var Receiver
diff --git a/Behavioral/Command/UndoableCommandInterface.php b/Behavioral/Command/UndoableCommandInterface.php
index 0fd101c..f9234ab 100644
--- a/Behavioral/Command/UndoableCommandInterface.php
+++ b/Behavioral/Command/UndoableCommandInterface.php
@@ -5,7 +5,7 @@ namespace DesignPatterns\Behavioral\Command;
 /**
  * Interface UndoableCommandInterface.
  */
-interface UndoableCommandInterface
+interface UndoableCommandInterface extends CommandInterface
 {
     /**
      * This method is used to undo change made by command execution