diff --git a/lib/csharp/src/Collections/THashSet.cs b/lib/csharp/src/Collections/THashSet.cs
index a995769..0ddea54 100644
--- a/lib/csharp/src/Collections/THashSet.cs
+++ b/lib/csharp/src/Collections/THashSet.cs
@@ -23,6 +23,7 @@
 
 namespace Thrift.Collections
 {
+     [Serializable]
 	public class THashSet<T> : ICollection<T>
 	{
 #if NET_2_0