diff --git a/protoc-c/c_field.cc b/protoc-c/c_field.cc
index d49c001..fc4943d 100644
--- a/protoc-c/c_field.cc
+++ b/protoc-c/c_field.cc
@@ -107,7 +107,7 @@ void FieldGenerator::GenerateDescriptorInitializerGeneric(io::Printer* printer,
 							  const std::string &descriptor_addr) const
 {
   std::map<std::string, std::string> variables;
-  const OneofDescriptor *oneof = descriptor_->containing_oneof();
+  const OneofDescriptor *oneof = descriptor_->real_containing_oneof();
   const ProtobufCFileOptions opt = descriptor_->file()->options().GetExtension(pb_c_file);
   variables["TYPE"] = type_macro;
   variables["classname"] = FullNameToC(FieldScope(descriptor_)->full_name(), FieldScope(descriptor_)->file());
diff --git a/protoc-c/c_generator.h b/protoc-c/c_generator.h
index b8b44aa..ceb53b2 100644
--- a/protoc-c/c_generator.h
+++ b/protoc-c/c_generator.h
@@ -93,6 +93,11 @@ class PROTOC_C_EXPORT CGenerator : public CodeGenerator {
                 const std::string& parameter,
                 OutputDirectory* output_directory,
                 std::string* error) const;
+
+  uint64_t GetSupportedFeatures() const override {
+    // Indicate that this code generator supports proto3 optional fields.
+    return FEATURE_PROTO3_OPTIONAL;
+  }
 };
 
 }  // namespace c
diff --git a/protoc-c/c_message.cc b/protoc-c/c_message.cc
index af2974c..34744f4 100755
--- a/protoc-c/c_message.cc
+++ b/protoc-c/c_message.cc
@@ -149,7 +149,7 @@ GenerateStructDefinition(io::Printer* printer) {
   }
 
   // Generate the case enums for unions
-  for (int i = 0; i < descriptor_->oneof_decl_count(); i++) {
+  for (int i = 0; i < descriptor_->real_oneof_decl_count(); i++) {
     const OneofDescriptor *oneof = descriptor_->oneof_decl(i);
     vars["opt_comma"] = ",";
 
@@ -191,7 +191,7 @@ GenerateStructDefinition(io::Printer* printer) {
   printer->Indent();
   for (int i = 0; i < descriptor_->field_count(); i++) {
     const FieldDescriptor *field = descriptor_->field(i);
-    if (field->containing_oneof() == NULL) {
+    if (field->real_containing_oneof() == NULL) {
       SourceLocation fieldSourceLoc;
       field->GetSourceLocation(&fieldSourceLoc);
 
@@ -202,7 +202,7 @@ GenerateStructDefinition(io::Printer* printer) {
   }
 
   // Generate unions from oneofs.
-  for (int i = 0; i < descriptor_->oneof_decl_count(); i++) {
+  for (int i = 0; i < descriptor_->real_oneof_decl_count(); i++) {
     const OneofDescriptor *oneof = descriptor_->oneof_decl(i);
     vars["oneofname"] = CamelToLower(oneof->name());
     vars["foneofname"] = FullNameToC(oneof->full_name(), oneof->file());
@@ -238,12 +238,12 @@ GenerateStructDefinition(io::Printer* printer) {
 		       " { PROTOBUF_C_MESSAGE_INIT (&$lcclassname$__descriptor) \\\n    ");
   for (int i = 0; i < descriptor_->field_count(); i++) {
     const FieldDescriptor *field = descriptor_->field(i);
-    if (field->containing_oneof() == NULL) {
+    if (field->real_containing_oneof() == NULL) {
       printer->Print(", ");
       field_generators_.get(field).GenerateStaticInit(printer);
     }
   }
-  for (int i = 0; i < descriptor_->oneof_decl_count(); i++) {
+  for (int i = 0; i < descriptor_->real_oneof_decl_count(); i++) {
     const OneofDescriptor *oneof = descriptor_->oneof_decl(i);
     vars["foneofname"] = FullNameToUpper(oneof->full_name(), oneof->file());
     // Initialize the case enum