diff --git a/src/google/protobuf/compiler/csharp/csharp_generator.cc b/src/google/protobuf/compiler/csharp/csharp_generator.cc
index df9730f898..c13ed65bec 100644
--- a/src/google/protobuf/compiler/csharp/csharp_generator.cc
+++ b/src/google/protobuf/compiler/csharp/csharp_generator.cc
@@ -81,6 +81,8 @@ bool Generator::Generate(
     } else if (options[i].first == "base_namespace") {
       cli_options.base_namespace = options[i].second;
       cli_options.base_namespace_specified = true;
+    } else if (options[i].first == "internal_access") {
+      cli_options.internal_access = true;
     } else {
       *error = "Unknown generator option: " + options[i].first;
       return false;
diff --git a/src/google/protobuf/compiler/csharp/csharp_options.h b/src/google/protobuf/compiler/csharp/csharp_options.h
index 9e5573cabe..f25812c87f 100644
--- a/src/google/protobuf/compiler/csharp/csharp_options.h
+++ b/src/google/protobuf/compiler/csharp/csharp_options.h
@@ -64,6 +64,9 @@ struct Options {
   // string, meaning "create a full directory hierarchy, starting from the first
   // segment of the namespace."
   bool base_namespace_specified;
+  // Whether the generated classes should have accessibility level of "internal".
+  // Defaults to false that generates "public" classes.
+  bool internal_access;
 };
 
 }  // namespace csharp
diff --git a/src/google/protobuf/compiler/csharp/csharp_source_generator_base.cc b/src/google/protobuf/compiler/csharp/csharp_source_generator_base.cc
index bd459dda13..16411e49c7 100644
--- a/src/google/protobuf/compiler/csharp/csharp_source_generator_base.cc
+++ b/src/google/protobuf/compiler/csharp/csharp_source_generator_base.cc
@@ -60,7 +60,7 @@ void SourceGeneratorBase::WriteGeneratedCodeAttributes(io::Printer* printer) {
 }
 
 std::string SourceGeneratorBase::class_access_level() {
-  return IsDescriptorProto(descriptor_) ? "internal" : "public";  // public_classes is always on.
+  return (IsDescriptorProto(descriptor_) || this->options()->internal_access) ? "internal" : "public";
 }
 
 const Options* SourceGeneratorBase::options() {