diff --git a/src/google/protobuf/compiler/csharp/csharp_generator.cc b/src/google/protobuf/compiler/csharp/csharp_generator.cc
index 0781cf810beb0..6418e61d395b0 100644
--- a/src/google/protobuf/compiler/csharp/csharp_generator.cc
+++ b/src/google/protobuf/compiler/csharp/csharp_generator.cc
@@ -59,6 +59,8 @@ bool Generator::Generate(const FileDescriptor* file,
       cli_options.serializable = true;
     } else if (options[i].first == "experimental_strip_nonfunctional_codegen") {
       cli_options.strip_nonfunctional_codegen = true;
+    } else if (options[i].first == "enable_nrt") {
+      cli_options.enable_nullable_reference_types = true;
     } else {
       *error = absl::StrCat("Unknown generator option: ", options[i].first);
       return false;
diff --git a/src/google/protobuf/compiler/csharp/csharp_message.cc b/src/google/protobuf/compiler/csharp/csharp_message.cc
index 9cc23761dc9f3..d5cb698e6e684 100644
--- a/src/google/protobuf/compiler/csharp/csharp_message.cc
+++ b/src/google/protobuf/compiler/csharp/csharp_message.cc
@@ -95,6 +95,7 @@ void MessageGenerator::Generate(io::Printer* printer) {
   absl::flat_hash_map<absl::string_view, std::string> vars;
   vars["class_name"] = class_name();
   vars["access_level"] = class_access_level();
+  vars["nrt_annotation"] = this->options()->enable_nullable_reference_types ? "?" : "";
 
   WriteMessageDocComment(printer, options(), descriptor_);
   AddDeprecatedFlag(printer);
@@ -122,7 +123,8 @@ void MessageGenerator::Generate(io::Printer* printer) {
       "private static readonly pb::MessageParser<$class_name$> _parser = new "
       "pb::MessageParser<$class_name$>(() => new $class_name$());\n");
 
-  printer->Print("private pb::UnknownFieldSet _unknownFields;\n");
+  printer->Print(vars,
+                "private pb::UnknownFieldSet$nrt_annotation$ _unknownFields;\n");
 
   if (has_extension_ranges_) {
     if (IsDescriptorProto(descriptor_->file())) {
@@ -419,16 +421,17 @@ void MessageGenerator::GenerateFreezingCode(io::Printer* printer) {}
 void MessageGenerator::GenerateFrameworkMethods(io::Printer* printer) {
   absl::flat_hash_map<absl::string_view, std::string> vars;
   vars["class_name"] = class_name();
+  vars["nrt_annotation"] = this->options()->enable_nullable_reference_types ? "?" : "";
 
   // Equality
   WriteGeneratedCodeAttributes(printer);
   printer->Print(vars,
-                 "public override bool Equals(object other) {\n"
+                 "public override bool Equals(object$nrt_annotation$ other) {\n"
                  "  return Equals(other as $class_name$);\n"
                  "}\n\n");
   WriteGeneratedCodeAttributes(printer);
   printer->Print(vars,
-                 "public bool Equals($class_name$ other) {\n"
+                 "public bool Equals($class_name$$nrt_annotation$ other) {\n"
                  "  if (ReferenceEquals(other, null)) {\n"
                  "    return false;\n"
                  "  }\n"
@@ -586,9 +589,10 @@ void MessageGenerator::GenerateMergingMethods(io::Printer* printer) {
   //   for code size.
   absl::flat_hash_map<absl::string_view, std::string> vars;
   vars["class_name"] = class_name();
+  vars["nrt_annotation"] = this->options()->enable_nullable_reference_types ? "?" : "";
 
   WriteGeneratedCodeAttributes(printer);
-  printer->Print(vars, "public void MergeFrom($class_name$ other) {\n");
+  printer->Print(vars, "public void MergeFrom($class_name$$nrt_annotation$ other) {\n");
   printer->Indent();
   printer->Print(
       "if (other == null) {\n"
diff --git a/src/google/protobuf/compiler/csharp/csharp_message_field.cc b/src/google/protobuf/compiler/csharp/csharp_message_field.cc
index 165118b969f44..a2cdf8b4430d5 100644
--- a/src/google/protobuf/compiler/csharp/csharp_message_field.cc
+++ b/src/google/protobuf/compiler/csharp/csharp_message_field.cc
@@ -30,6 +30,7 @@ MessageFieldGenerator::MessageFieldGenerator(const FieldDescriptor* descriptor,
     variables_["has_property_check"] = absl::StrCat(name(), "_ != null");
     variables_["has_not_property_check"] = absl::StrCat(name(), "_ == null");
   }
+  variables_["nrt_annotation"] = this->options()->enable_nullable_reference_types ? "?" : "";
 }
 
 MessageFieldGenerator::~MessageFieldGenerator() {
@@ -44,7 +45,7 @@ void MessageFieldGenerator::GenerateMembers(io::Printer* printer) {
   AddPublicMemberAttributes(printer);
   printer->Print(
     variables_,
-    "$access_level$ $type_name$ $property_name$ {\n"
+    "$access_level$ $type_name$$nrt_annotation$ $property_name$ {\n"
     "  get { return $name$_; }\n"
     "  set {\n"
     "    $name$_ = value;\n"
diff --git a/src/google/protobuf/compiler/csharp/csharp_options.h b/src/google/protobuf/compiler/csharp/csharp_options.h
index 4c034d53600a6..de93f90df90fe 100644
--- a/src/google/protobuf/compiler/csharp/csharp_options.h
+++ b/src/google/protobuf/compiler/csharp/csharp_options.h
@@ -23,7 +23,8 @@ struct Options {
         base_namespace_specified(false),
         internal_access(false),
         serializable(false),
-        strip_nonfunctional_codegen(false) {}
+        strip_nonfunctional_codegen(false),
+        enable_nullable_reference_types(false) {}
   // Extension of the generated file. Defaults to ".cs"
   std::string file_extension;
   // Base namespace to use to create directory hierarchy. Defaults to "".
@@ -50,6 +51,9 @@ struct Options {
   bool serializable;
   // If true, strip out nonfunctional codegen.
   bool strip_nonfunctional_codegen;
+  //  Whether the generated files support null reference types. 
+  // Defaults to false
+  bool enable_nullable_reference_types;
 };
 
 }  // namespace csharp
diff --git a/src/google/protobuf/compiler/csharp/csharp_reflection_class.cc b/src/google/protobuf/compiler/csharp/csharp_reflection_class.cc
index 1e8d3f282558c..63e3fe6e64f49 100644
--- a/src/google/protobuf/compiler/csharp/csharp_reflection_class.cc
+++ b/src/google/protobuf/compiler/csharp/csharp_reflection_class.cc
@@ -105,7 +105,16 @@ void ReflectionClassGenerator::WriteIntroduction(io::Printer* printer) {
     "// <auto-generated>\n"
     "//     Generated by the protocol buffer compiler.  DO NOT EDIT!\n"
     "//     source: $file_name$\n"
-    "// </auto-generated>\n"
+    "// </auto-generated>\n",
+     "file_name", file_->name());
+
+  if (this->options()->enable_nullable_reference_types) {
+    printer->Print(
+      "#nullable enable annotations\n", 
+      "file_name", file_->name());
+  }
+
+  printer->Print(
     "#pragma warning disable 1591, 0612, 3021, 8981\n"
     "#region Designer generated code\n"
     "\n"