diff --git a/src/test/java/com/flowingcode/vaadin/addons/twincolgrid/Book.java b/src/test/java/com/flowingcode/vaadin/addons/twincolgrid/Book.java
index 66719b7..38298f7 100644
--- a/src/test/java/com/flowingcode/vaadin/addons/twincolgrid/Book.java
+++ b/src/test/java/com/flowingcode/vaadin/addons/twincolgrid/Book.java
@@ -19,9 +19,11 @@
  */
 package com.flowingcode.vaadin.addons.twincolgrid;
 
+import java.io.Serializable;
 import java.util.Objects;
 
-public class Book {
+@SuppressWarnings("serial")
+public class Book implements Serializable {
 
   private final String isbn;
 
diff --git a/src/test/java/com/flowingcode/vaadin/addons/twincolgrid/Library.java b/src/test/java/com/flowingcode/vaadin/addons/twincolgrid/Library.java
index d86c6ad..832901e 100644
--- a/src/test/java/com/flowingcode/vaadin/addons/twincolgrid/Library.java
+++ b/src/test/java/com/flowingcode/vaadin/addons/twincolgrid/Library.java
@@ -19,9 +19,11 @@
  */
 package com.flowingcode.vaadin.addons.twincolgrid;
 
+import java.io.Serializable;
 import java.util.List;
 
-public class Library {
+@SuppressWarnings("serial")
+public class Library implements Serializable {
 
   private final String name;