diff --git a/src/main/java/com/avaje/ebeaninternal/server/cache/CachedManyIds.java b/src/main/java/com/avaje/ebeaninternal/server/cache/CachedManyIds.java
index 250c978a3..069057a6f 100644
--- a/src/main/java/com/avaje/ebeaninternal/server/cache/CachedManyIds.java
+++ b/src/main/java/com/avaje/ebeaninternal/server/cache/CachedManyIds.java
@@ -1,6 +1,11 @@
 package com.avaje.ebeaninternal.server.cache;
 
+import java.io.Externalizable;
+import java.io.IOException;
+import java.io.ObjectInput;
+import java.io.ObjectOutput;
 import java.io.Serializable;
+import java.util.ArrayList;
 import java.util.List;
 
 /**
@@ -9,14 +14,37 @@ import java.util.List;
  * This is effectively just the Id values for each of the beans in the collection.
  * </p>
  */
-public class CachedManyIds implements Serializable {
+public class CachedManyIds implements Externalizable {
 
-  private final List<Object> idList;
+  private List<Object> idList;
 
   public CachedManyIds(List<Object> idList) {
     this.idList = idList;
   }
 
+  /**
+   * Construct for serialization.
+   */
+  public CachedManyIds() {
+  }
+
+  @Override
+  public void writeExternal(ObjectOutput out) throws IOException {
+    out.writeInt(idList.size());
+    for (Object id : idList) {
+      out.writeObject(id);
+    }
+  }
+
+  @Override
+  public void readExternal(ObjectInput in) throws IOException, ClassNotFoundException {
+    int size = in.readInt();
+    idList = new ArrayList<Object>(size);
+    for (int i = 0; i < size; i++) {
+      idList.add(in.readObject());
+    }
+  }
+
   public String toString() {
     return idList.toString();
   }