diff --git a/src/main/java/com/flowingcode/vaadin/addons/demo/DemoHelperViewer.java b/src/main/java/com/flowingcode/vaadin/addons/demo/DemoHelperViewer.java
index 3ce98ac..3d0e733 100644
--- a/src/main/java/com/flowingcode/vaadin/addons/demo/DemoHelperViewer.java
+++ b/src/main/java/com/flowingcode/vaadin/addons/demo/DemoHelperViewer.java
@@ -20,13 +20,14 @@
 package com.flowingcode.vaadin.addons.demo;
 
 import com.vaadin.flow.component.Component;
+import java.io.Serializable;
 
 /**
  * Implementations of this interface can be used to display content rendered by
  * {@link DemoHelperRenderer}.
  *
  */
-public interface DemoHelperViewer {
+public interface DemoHelperViewer extends Serializable {
 
   /**
    * Shows help content.
diff --git a/src/main/java/com/flowingcode/vaadin/addons/demo/DialogDemoHelperViewer.java b/src/main/java/com/flowingcode/vaadin/addons/demo/DialogDemoHelperViewer.java
index 7528563..86e727d 100644
--- a/src/main/java/com/flowingcode/vaadin/addons/demo/DialogDemoHelperViewer.java
+++ b/src/main/java/com/flowingcode/vaadin/addons/demo/DialogDemoHelperViewer.java
@@ -27,6 +27,7 @@
  * {@link Dialog}.
  * 
  */
+@SuppressWarnings("serial")
 public class DialogDemoHelperViewer implements DemoHelperViewer {
 
   @Override