diff --git a/lib/csharp/src/Collections/THashSet.cs b/lib/csharp/src/Collections/THashSet.cs
index 0ddea54..e2fc8b5 100644
--- a/lib/csharp/src/Collections/THashSet.cs
+++ b/lib/csharp/src/Collections/THashSet.cs
@@ -23,11 +23,13 @@
 
 namespace Thrift.Collections
 {
+#if !SILVERLIGHT
      [Serializable]
+#endif
 	public class THashSet<T> : ICollection<T>
 	{
-#if NET_2_0
-		TDictSet<T> set = new TDictSet<T>();
+#if NET_2_0 || SILVERLIGHT
+        TDictSet<T> set = new TDictSet<T>();
 #else
 		HashSet<T> set = new HashSet<T>();
 #endif
@@ -76,8 +78,8 @@
 			return set.Remove(item);
 		}
 
-#if NET_2_0
-		private class TDictSet<V> : ICollection<V>
+#if NET_2_0 || SILVERLIGHT
+        private class TDictSet<V> : ICollection<V>
 		{
 			Dictionary<V, TDictSet<V>> dict = new Dictionary<V, TDictSet<V>>();