Support Compact Framework 3.5
diff --git a/src/ProtocolBuffers/UnknownFieldSet.cs b/src/ProtocolBuffers/UnknownFieldSet.cs
index 2a955fc..49c1fa3 100644
--- a/src/ProtocolBuffers/UnknownFieldSet.cs
+++ b/src/ProtocolBuffers/UnknownFieldSet.cs
@@ -243,11 +243,10 @@
public sealed class Builder
{
/// <summary>
- /// Mapping from number to field. Note that by using a SortedDictionary we ensure
+ /// Mapping from number to field. Note that by using a SortedList we ensure
/// that the fields will be serialized in ascending order.
/// </summary>
- private IDictionary<int, UnknownField> fields = new SortedDictionary<int, UnknownField>();
-
+ private IDictionary<int, UnknownField> fields = new SortedList<int, UnknownField>();
// Optimization: We keep around a builder for the last field that was
// modified so that we can efficiently add to it multiple times in a
// row (important when parsing an unknown repeated field).