diff --git a/lib/csharp/src/Net35/ExtensionsNet35.cs b/lib/csharp/src/Net35/ExtensionsNet35.cs
new file mode 100644
index 0000000..73a4232
--- /dev/null
+++ b/lib/csharp/src/Net35/ExtensionsNet35.cs
@@ -0,0 +1,31 @@
+﻿using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+using System.Text;
+
+#if (!NET45)
+namespace Thrift
+{
+    static class StreamExtensionsNet35
+    {
+        // CopyTo() has been added in 4.0
+        public static long CopyTo(this Stream source, Stream target)
+        {
+            byte[] buffer = new byte[8192];  // multiple of 4096
+            long nTotal = 0;
+            while (true)
+            {
+                int nRead = source.Read(buffer, 0, buffer.Length);
+                if (nRead <= 0)  // done?
+                    return nTotal;
+
+                target.Write(buffer, 0, nRead);
+                nTotal += nRead;
+            }
+        }
+    }
+
+}
+#endif
+