diff --git a/lib/protoc.exe b/lib/protoc.exe
index d408e9ed57..efda94d62d 100644
Binary files a/lib/protoc.exe and b/lib/protoc.exe differ
diff --git a/protos/google/protobuf/csharp_options.proto b/protos/google/protobuf/csharp_options.proto
index 41deafa304..b58a549172 100644
--- a/protos/google/protobuf/csharp_options.proto
+++ b/protos/google/protobuf/csharp_options.proto
@@ -6,10 +6,11 @@ package google.protobuf;
 
 message CSharpFileOptions {
   optional string namespace = 1;
-  optional string umbrella_classname= 2;
-  optional bool public_classes = 3;
+  optional string umbrella_classname = 2;
+  optional bool public_classes = 3 [default = true];
   optional bool multiple_files = 4;
   optional bool nest_classes = 5;
+  optional bool code_contracts = 6;
 }
 
 extend FileOptions {
diff --git a/src/ProtoGen/UmbrellaClassGenerator.cs b/src/ProtoGen/UmbrellaClassGenerator.cs
index d41e70eb1c..9dcbcab906 100644
--- a/src/ProtoGen/UmbrellaClassGenerator.cs
+++ b/src/ProtoGen/UmbrellaClassGenerator.cs
@@ -115,8 +115,10 @@ namespace Google.ProtocolBuffers.ProtoGen {
         writer.WriteLine("namespace {0} {{", Descriptor.CSharpOptions.Namespace);
         writer.Indent();
         writer.WriteLine();
+      }    
+      if (Descriptor.CSharpOptions.CodeContracts) {
+          writer.WriteLine("[global::System.Diagnostics.Contracts.ContractVerificationAttribute(false)]");
       }
-
       writer.WriteLine("{0} static partial class {1} {{", ClassAccessLevel, Descriptor.CSharpOptions.UmbrellaClassname);
       writer.WriteLine();
       writer.Indent();
diff --git a/src/ProtocolBuffers/DescriptorProtos/CSharpOptions.cs b/src/ProtocolBuffers/DescriptorProtos/CSharpOptions.cs
index 0185870680..9ab99dfe32 100644
--- a/src/ProtocolBuffers/DescriptorProtos/CSharpOptions.cs
+++ b/src/ProtocolBuffers/DescriptorProtos/CSharpOptions.cs
@@ -37,21 +37,22 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       byte[] descriptorData = global::System.Convert.FromBase64String(
           "CiRnb29nbGUvcHJvdG9idWYvY3NoYXJwX29wdGlvbnMucHJvdG8SD2dvb2ds" + 
           "ZS5wcm90b2J1ZhogZ29vZ2xlL3Byb3RvYnVmL2Rlc2NyaXB0b3IucHJvdG8i" + 
-          "iAEKEUNTaGFycEZpbGVPcHRpb25zEhEKCW5hbWVzcGFjZRgBIAEoCRIaChJ1" + 
-          "bWJyZWxsYV9jbGFzc25hbWUYAiABKAkSFgoOcHVibGljX2NsYXNzZXMYAyAB" + 
-          "KAgSFgoObXVsdGlwbGVfZmlsZXMYBCABKAgSFAoMbmVzdF9jbGFzc2VzGAUg" + 
-          "ASgIIisKEkNTaGFycEZpZWxkT3B0aW9ucxIVCg1wcm9wZXJ0eV9uYW1lGAEg" + 
-          "ASgJOl4KE2NzaGFycF9maWxlX29wdGlvbnMSHC5nb29nbGUucHJvdG9idWYu" + 
-          "RmlsZU9wdGlvbnMY6AcgASgLMiIuZ29vZ2xlLnByb3RvYnVmLkNTaGFycEZp" + 
-          "bGVPcHRpb25zOmEKFGNzaGFycF9maWVsZF9vcHRpb25zEh0uZ29vZ2xlLnBy" + 
-          "b3RvYnVmLkZpZWxkT3B0aW9ucxjoByABKAsyIy5nb29nbGUucHJvdG9idWYu" + 
-          "Q1NoYXJwRmllbGRPcHRpb25z");
+          "pgEKEUNTaGFycEZpbGVPcHRpb25zEhEKCW5hbWVzcGFjZRgBIAEoCRIaChJ1" + 
+          "bWJyZWxsYV9jbGFzc25hbWUYAiABKAkSHAoOcHVibGljX2NsYXNzZXMYAyAB" + 
+          "KAg6BHRydWUSFgoObXVsdGlwbGVfZmlsZXMYBCABKAgSFAoMbmVzdF9jbGFz" + 
+          "c2VzGAUgASgIEhYKDmNvZGVfY29udHJhY3RzGAYgASgIIisKEkNTaGFycEZp" + 
+          "ZWxkT3B0aW9ucxIVCg1wcm9wZXJ0eV9uYW1lGAEgASgJOl4KE2NzaGFycF9m" + 
+          "aWxlX29wdGlvbnMSHC5nb29nbGUucHJvdG9idWYuRmlsZU9wdGlvbnMY6Acg" + 
+          "ASgLMiIuZ29vZ2xlLnByb3RvYnVmLkNTaGFycEZpbGVPcHRpb25zOmEKFGNz" + 
+          "aGFycF9maWVsZF9vcHRpb25zEh0uZ29vZ2xlLnByb3RvYnVmLkZpZWxkT3B0" + 
+          "aW9ucxjoByABKAsyIy5nb29nbGUucHJvdG9idWYuQ1NoYXJwRmllbGRPcHRp" + 
+          "b25z");
       pbd::FileDescriptor.InternalDescriptorAssigner assigner = delegate(pbd::FileDescriptor root) {
         descriptor = root;
         internal__static_google_protobuf_CSharpFileOptions__Descriptor = Descriptor.MessageTypes[0];
         internal__static_google_protobuf_CSharpFileOptions__FieldAccessorTable = 
             new pb::FieldAccess.FieldAccessorTable<global::Google.ProtocolBuffers.DescriptorProtos.CSharpFileOptions, global::Google.ProtocolBuffers.DescriptorProtos.CSharpFileOptions.Builder>(internal__static_google_protobuf_CSharpFileOptions__Descriptor,
-                new string[] { "Namespace", "UmbrellaClassname", "PublicClasses", "MultipleFiles", "NestClasses", });
+                new string[] { "Namespace", "UmbrellaClassname", "PublicClasses", "MultipleFiles", "NestClasses", "CodeContracts", });
         internal__static_google_protobuf_CSharpFieldOptions__Descriptor = Descriptor.MessageTypes[1];
         internal__static_google_protobuf_CSharpFieldOptions__FieldAccessorTable = 
             new pb::FieldAccess.FieldAccessorTable<global::Google.ProtocolBuffers.DescriptorProtos.CSharpFieldOptions, global::Google.ProtocolBuffers.DescriptorProtos.CSharpFieldOptions.Builder>(internal__static_google_protobuf_CSharpFieldOptions__Descriptor,
@@ -113,7 +114,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
     
     public const int PublicClassesFieldNumber = 3;
     private bool hasPublicClasses;
-    private bool publicClasses_ = false;
+    private bool publicClasses_ = true;
     public bool HasPublicClasses {
       get { return hasPublicClasses; }
     }
@@ -141,6 +142,16 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       get { return nestClasses_; }
     }
     
+    public const int CodeContractsFieldNumber = 6;
+    private bool hasCodeContracts;
+    private bool codeContracts_ = false;
+    public bool HasCodeContracts {
+      get { return hasCodeContracts; }
+    }
+    public bool CodeContracts {
+      get { return codeContracts_; }
+    }
+    
     public override bool IsInitialized {
       get {
         return true;
@@ -163,6 +174,9 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       if (HasNestClasses) {
         output.WriteBool(5, NestClasses);
       }
+      if (HasCodeContracts) {
+        output.WriteBool(6, CodeContracts);
+      }
       UnknownFields.WriteTo(output);
     }
     
@@ -188,6 +202,9 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         if (HasNestClasses) {
           size += pb::CodedOutputStream.ComputeBoolSize(5, NestClasses);
         }
+        if (HasCodeContracts) {
+          size += pb::CodedOutputStream.ComputeBoolSize(6, CodeContracts);
+        }
         size += UnknownFields.SerializedSize;
         memoizedSerializedSize = size;
         return size;
@@ -295,6 +312,9 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         if (other.HasNestClasses) {
           NestClasses = other.NestClasses;
         }
+        if (other.HasCodeContracts) {
+          CodeContracts = other.CodeContracts;
+        }
         this.MergeUnknownFields(other.UnknownFields);
         return this;
       }
@@ -347,6 +367,10 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
               NestClasses = input.ReadBool();
               break;
             }
+            case 48: {
+              CodeContracts = input.ReadBool();
+              break;
+            }
           }
         }
       }
@@ -404,7 +428,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }
       public Builder ClearPublicClasses() {
         result.hasPublicClasses = false;
-        result.publicClasses_ = false;
+        result.publicClasses_ = true;
         return this;
       }
       
@@ -443,6 +467,24 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         result.nestClasses_ = false;
         return this;
       }
+      
+      public bool HasCodeContracts {
+        get { return result.HasCodeContracts; }
+      }
+      public bool CodeContracts {
+        get { return result.CodeContracts; }
+        set { SetCodeContracts(value); }
+      }
+      public Builder SetCodeContracts(bool value) {
+        result.hasCodeContracts = true;
+        result.codeContracts_ = value;
+        return this;
+      }
+      public Builder ClearCodeContracts() {
+        result.hasCodeContracts = false;
+        result.codeContracts_ = false;
+        return this;
+      }
     }
     static CSharpFileOptions() {
       object.ReferenceEquals(global::Google.ProtocolBuffers.DescriptorProtos.CSharpOptions.Descriptor, null);
diff --git a/src/ProtocolBuffers/Descriptors/FileDescriptor.cs b/src/ProtocolBuffers/Descriptors/FileDescriptor.cs
index a6dd7f85e0..4d7b54e080 100644
--- a/src/ProtocolBuffers/Descriptors/FileDescriptor.cs
+++ b/src/ProtocolBuffers/Descriptors/FileDescriptor.cs
@@ -94,15 +94,6 @@ namespace Google.ProtocolBuffers.Descriptors {
       if (!builder.HasNamespace) {
         builder.Namespace = Package;
       }
-      if (!builder.HasMultipleFiles) {
-        builder.MultipleFiles = false;
-      }
-      if (!builder.HasNestClasses) {
-        builder.NestClasses = false;
-      }
-      if (!builder.HasPublicClasses) {
-        builder.PublicClasses = true;
-      }
       if (!builder.HasUmbrellaClassname) {
         int lastSlash = Name.LastIndexOf('/');
         string baseName = Name.Substring(lastSlash + 1);
diff --git a/src/ProtocolBuffers/Descriptors/MessageDescriptor.cs b/src/ProtocolBuffers/Descriptors/MessageDescriptor.cs
index cdd75a0cac..79356170e7 100644
--- a/src/ProtocolBuffers/Descriptors/MessageDescriptor.cs
+++ b/src/ProtocolBuffers/Descriptors/MessageDescriptor.cs
@@ -57,6 +57,7 @@ namespace Google.ProtocolBuffers.Descriptors {
       enumTypes = DescriptorUtil.ConvertAndMakeReadOnly(proto.EnumTypeList,
           (type, index) => new EnumDescriptor(type, file, this, index));
 
+      // TODO(jonskeet): Sort fields first?
       fields = DescriptorUtil.ConvertAndMakeReadOnly(proto.FieldList,
           (field, index) => new FieldDescriptor(field, file, this, index, false));