diff --git a/src/org/forkalsrud/album/web/AlbumServlet.java b/src/org/forkalsrud/album/web/AlbumServlet.java
index aa3bcf8..32d9de1 100644
--- a/src/org/forkalsrud/album/web/AlbumServlet.java
+++ b/src/org/forkalsrud/album/web/AlbumServlet.java
@@ -7,6 +7,7 @@ import java.awt.image.BufferedImage;
 import java.io.ByteArrayOutputStream;
 import java.io.File;
 import java.io.IOException;
+import java.io.Serializable;
 import java.util.Iterator;
 
 import javax.imageio.ImageIO;
@@ -21,12 +22,12 @@ import javax.servlet.http.HttpServlet;
 import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpServletResponse;
 
-import org.apache.commons.logging.LogFactory;
-import org.apache.log4j.PropertyConfigurator;
 import net.sf.ehcache.Cache;
 import net.sf.ehcache.CacheManager;
 import net.sf.ehcache.Element;
 
+import org.apache.commons.logging.LogFactory;
+import org.apache.log4j.PropertyConfigurator;
 import org.forkalsrud.album.exif.Dimension;
 import org.forkalsrud.album.exif.DirectoryEntry;
 import org.forkalsrud.album.exif.Entry;
@@ -316,7 +317,7 @@ public class AlbumServlet
     	}
     }
 
-    static class CachedImage {
+    static class CachedImage implements Serializable {
         long lastModified;
         String mimeType;
         byte[] bits;