Extracted ICodedInputStream interface
diff --git a/src/ProtocolBuffers/ExtendableBuilder.cs b/src/ProtocolBuffers/ExtendableBuilder.cs
index 49265f4..cbe203d 100644
--- a/src/ProtocolBuffers/ExtendableBuilder.cs
+++ b/src/ProtocolBuffers/ExtendableBuilder.cs
@@ -130,7 +130,7 @@
         /// </summary>

         /// <returns>true unless the tag is an end-group tag</returns>

         [CLSCompliant(false)]

-        protected override bool ParseUnknownField(CodedInputStream input, UnknownFieldSet.Builder unknownFields,

+        protected override bool ParseUnknownField(ICodedInputStream input, UnknownFieldSet.Builder unknownFields,

                                                   ExtensionRegistry extensionRegistry, uint tag, string fieldName)

         {

             return unknownFields.MergeFieldFrom(input, extensionRegistry, this, tag, fieldName);