diff --git a/protobuf/lib/src/protobuf/extension_field_set.dart b/protobuf/lib/src/protobuf/extension_field_set.dart
index 5b7e1c92e..cad43e9ed 100644
--- a/protobuf/lib/src/protobuf/extension_field_set.dart
+++ b/protobuf/lib/src/protobuf/extension_field_set.dart
@@ -6,11 +6,20 @@ part of protobuf;
 
 class _ExtensionFieldSet {
   final _FieldSet _parent;
-  final Map<int, Extension> _info = <int, Extension>{};
-  final Map<int, dynamic> _values = <int, dynamic>{};
-  bool _isReadOnly = false;
 
-  _ExtensionFieldSet(this._parent);
+  final Map<int, Extension> _info;
+
+  final Map<int, dynamic> _values;
+
+  bool _isReadOnly;
+
+  _ExtensionFieldSet(this._parent)
+      : _info = <int, Extension>{},
+        _values = <int, dynamic>{},
+        _isReadOnly = false;
+
+  _ExtensionFieldSet._(
+      this._parent, this._info, this._values, this._isReadOnly);
 
   Extension? _getInfoOrNull(int tagNumber) => _info[tagNumber];
 
@@ -203,4 +212,66 @@ class _ExtensionFieldSet {
           'use `ExtensionRegistry.reparseMessage`.');
     }
   }
+
+  _ExtensionFieldSet deepCopy(_FieldSet parent, {bool freeze = false}) {
+    final values = <int, dynamic>{};
+
+    for (final entry in _values.entries) {
+      final key = entry.key;
+      final value = entry.value;
+      final fieldInfo = _info[key]!;
+
+      if (fieldInfo.isRepeated) {
+        final repeated = fieldInfo._createRepeatedField(parent._message!);
+        values[key] = repeated;
+
+        if (_isGroupOrMessage(fieldInfo.type)) {
+          final List<GeneratedMessage> listValue = value;
+          for (final message in listValue) {
+            repeated.add(message.deepCopy());
+          }
+          // repeated.addAll(listValue.map((message) => message.deepCopy()));
+        } else {
+          final List<dynamic> listValue = value;
+          repeated.addAll(listValue);
+        }
+
+        continue;
+      }
+
+      if (fieldInfo.isMapField) {
+        final MapFieldInfo<dynamic, dynamic> mapFieldInfo =
+            fieldInfo as dynamic;
+        final map = mapFieldInfo._createMapField(parent._message!);
+        values[key] = map;
+
+        if (_isGroupOrMessage(mapFieldInfo.valueFieldType)) {
+          Map<dynamic, GeneratedMessage> mapValue = value;
+          for (final entry in mapValue.entries) {
+            map[entry.key] = entry.value.deepCopy();
+          }
+        } else {
+          Map<dynamic, dynamic> mapValue = value;
+          map.addAll(mapValue);
+        }
+
+        continue;
+      }
+
+      if (fieldInfo.isGroupOrMessage) {
+        final GeneratedMessage messageValue = value;
+        values[key] = messageValue.deepCopy(freeze: freeze);
+        continue;
+      }
+
+      values[key] = value;
+    }
+
+    return _ExtensionFieldSet._(
+      parent,
+      _info,
+      values,
+      freeze,
+    );
+  }
 }
diff --git a/protobuf/lib/src/protobuf/field_set.dart b/protobuf/lib/src/protobuf/field_set.dart
index ed8394e57..c80258142 100644
--- a/protobuf/lib/src/protobuf/field_set.dart
+++ b/protobuf/lib/src/protobuf/field_set.dart
@@ -78,6 +78,9 @@ class _FieldSet {
       : _values = _makeValueList(meta.byIndex.length),
         _oneofCases = meta.oneofs.isEmpty ? null : <int, int>{};
 
+  _FieldSet._(this._message, this._eventPlugin, this._values, this._extensions,
+      this._unknownFields, this._frozenState, this._oneofCases);
+
   static List _makeValueList(int length) {
     if (length == 0) return _zeroList;
     return List.filled(length, null, growable: false);
@@ -905,4 +908,79 @@ class _FieldSet {
 
     _oneofCases?.addAll(original._oneofCases!);
   }
+
+  _FieldSet deepCopy(GeneratedMessage message, EventPlugin? eventPlugin,
+      {bool freeze = false}) {
+    final values = _makeValueList(_values.length);
+    final meta = _meta;
+
+    for (var valueIdx = 0; valueIdx < _values.length; valueIdx += 1) {
+      final value = _values[valueIdx];
+
+      if (value == null) {
+        continue;
+      }
+
+      final fieldInfo = meta.byIndex[valueIdx];
+
+      if (fieldInfo.isRepeated) {
+        final repeated = fieldInfo._createRepeatedField(message);
+        values[valueIdx] = repeated;
+
+        if (_isGroupOrMessage(fieldInfo.type)) {
+          final List<GeneratedMessage> listValue = value;
+          for (final message in listValue) {
+            repeated.add(message.deepCopy());
+          }
+          // repeated.addAll(listValue.map((message) => message.deepCopy()));
+        } else {
+          final List<dynamic> listValue = value;
+          repeated.addAll(listValue);
+        }
+
+        continue;
+      }
+
+      if (fieldInfo.isMapField) {
+        final MapFieldInfo<dynamic, dynamic> mapFieldInfo =
+            fieldInfo as dynamic;
+        final map = mapFieldInfo._createMapField(message);
+        values[valueIdx] = map;
+
+        if (_isGroupOrMessage(mapFieldInfo.valueFieldType)) {
+          Map<dynamic, GeneratedMessage> mapValue = value;
+          for (final entry in mapValue.entries) {
+            map[entry.key] = entry.value.deepCopy();
+          }
+        } else {
+          Map<dynamic, dynamic> mapValue = value;
+          map.addAll(mapValue);
+        }
+
+        continue;
+      }
+
+      if (fieldInfo.isGroupOrMessage) {
+        final GeneratedMessage messageValue = value;
+        values[valueIdx] = messageValue.deepCopy(freeze: freeze);
+        continue;
+      }
+
+      values[valueIdx] = value;
+    }
+
+    final copy = _FieldSet._(
+      message,
+      eventPlugin,
+      values,
+      null,
+      _unknownFields?.deepCopy(freeze: freeze),
+      freeze, // TODO: Can we use `_frozenState` here?
+      _oneofCases == null ? null : Map.from(_oneofCases!),
+    );
+
+    copy._extensions = _extensions?.deepCopy(copy, freeze: freeze);
+
+    return copy;
+  }
 }
diff --git a/protobuf/lib/src/protobuf/generated_message.dart b/protobuf/lib/src/protobuf/generated_message.dart
index c77a17e2e..b47b28c8a 100644
--- a/protobuf/lib/src/protobuf/generated_message.dart
+++ b/protobuf/lib/src/protobuf/generated_message.dart
@@ -578,5 +578,11 @@ extension GeneratedMessageGenericExtensions<T extends GeneratedMessage> on T {
   }
 
   /// Returns a writable deep copy of this message.
-  T deepCopy() => info_.createEmptyInstance!() as T..mergeFromMessage(this);
+  T deepCopy({bool freeze = false}) {
+    final T message = info_.createEmptyInstance!() as dynamic;
+    final eventPlugin = message.eventPlugin;
+    message.__fieldSet =
+        __fieldSet?.deepCopy(message, eventPlugin, freeze: freeze);
+    return message;
+  }
 }
diff --git a/protobuf/lib/src/protobuf/pb_list.dart b/protobuf/lib/src/protobuf/pb_list.dart
index 3c17c4791..e13480590 100644
--- a/protobuf/lib/src/protobuf/pb_list.dart
+++ b/protobuf/lib/src/protobuf/pb_list.dart
@@ -14,13 +14,14 @@ class PbList<E> extends ListBase<E> {
   final List<E> _wrappedList;
   final CheckFunc<E> _check;
 
-  bool _isReadOnly = false;
+  bool _isReadOnly;
 
   bool get isFrozen => _isReadOnly;
 
   PbList({CheckFunc<E> check = _checkNotNull})
       : _wrappedList = <E>[],
-        _check = check;
+        _check = check,
+        _isReadOnly = false;
 
   PbList.unmodifiable()
       : _wrappedList = const [],
@@ -29,7 +30,8 @@ class PbList<E> extends ListBase<E> {
 
   PbList.from(List from)
       : _wrappedList = List<E>.from(from),
-        _check = _checkNotNull;
+        _check = _checkNotNull,
+        _isReadOnly = false;
 
   @override
   void add(E element) {
diff --git a/protobuf/lib/src/protobuf/unknown_field_set.dart b/protobuf/lib/src/protobuf/unknown_field_set.dart
index 5e000581f..95433f83d 100644
--- a/protobuf/lib/src/protobuf/unknown_field_set.dart
+++ b/protobuf/lib/src/protobuf/unknown_field_set.dart
@@ -8,11 +8,15 @@ part of protobuf;
 class UnknownFieldSet {
   static final UnknownFieldSet emptyUnknownFieldSet = UnknownFieldSet()
     .._markReadOnly();
-  final Map<int, UnknownFieldSetField> _fields = <int, UnknownFieldSetField>{};
 
-  UnknownFieldSet();
+  final Map<int, UnknownFieldSetField> _fields;
 
-  UnknownFieldSet._clone(UnknownFieldSet unknownFieldSet) {
+  UnknownFieldSet() : _fields = <int, UnknownFieldSetField>{};
+
+  UnknownFieldSet._(this._fields, this._isReadOnly);
+
+  UnknownFieldSet._clone(UnknownFieldSet unknownFieldSet)
+      : _fields = <int, UnknownFieldSetField>{} {
     mergeFromUnknownFieldSet(unknownFieldSet);
   }
 
@@ -195,15 +199,37 @@ class UnknownFieldSet {
       _throwFrozenMessageModificationError('UnknownFieldSet', methodName);
     }
   }
+
+  UnknownFieldSet deepCopy({bool freeze = false}) {
+    final fields = <int, UnknownFieldSetField>{};
+
+    for (final entry in _fields.entries) {
+      final key = entry.key;
+      final value = entry.value;
+      fields[key] = value.deepCopy(freeze: freeze);
+    }
+
+    return UnknownFieldSet._(fields, freeze);
+  }
 }
 
 /// An unknown field in a [UnknownFieldSet].
 class UnknownFieldSetField {
-  List<List<int>> _lengthDelimited = <List<int>>[];
-  List<Int64> _varints = <Int64>[];
-  List<int> _fixed32s = <int>[];
-  List<Int64> _fixed64s = <Int64>[];
-  List<UnknownFieldSet> _groups = <UnknownFieldSet>[];
+  List<List<int>> _lengthDelimited;
+  List<Int64> _varints;
+  List<int> _fixed32s;
+  List<Int64> _fixed64s;
+  List<UnknownFieldSet> _groups;
+
+  UnknownFieldSetField()
+      : _lengthDelimited = <List<int>>[],
+        _varints = <Int64>[],
+        _fixed32s = <int>[],
+        _fixed64s = <Int64>[],
+        _groups = <UnknownFieldSet>[];
+
+  UnknownFieldSetField._(this._lengthDelimited, this._varints, this._fixed32s,
+      this._fixed64s, this._groups);
 
   List<List<int>> get lengthDelimited => _lengthDelimited;
   List<Int64> get varints => _varints;
@@ -309,4 +335,14 @@ class UnknownFieldSetField {
   void addVarint(Int64 value) {
     varints.add(value);
   }
+
+  UnknownFieldSetField deepCopy({bool freeze = false}) {
+    return UnknownFieldSetField._(
+      _lengthDelimited.map((List<int> e) => List<int>.from(e)).toList(),
+      List.from(_varints),
+      List.from(_fixed32s),
+      List.from(_fixed64s),
+      List.from(_groups.map((e) => e.deepCopy(freeze: freeze))),
+    );
+  }
 }
diff --git a/protoc_plugin/lib/src/generated/dart_options.pb.dart b/protoc_plugin/lib/src/generated/dart_options.pb.dart
index b69d0f042..f895e4801 100644
--- a/protoc_plugin/lib/src/generated/dart_options.pb.dart
+++ b/protoc_plugin/lib/src/generated/dart_options.pb.dart
@@ -47,7 +47,7 @@ class DartMixin extends $pb.GeneratedMessage {
   @$core.Deprecated('Using this can add significant overhead to your binary. '
       'Use [GeneratedMessageGenericExtensions.deepCopy] instead. '
       'Will be removed in next major version')
-  DartMixin clone() => DartMixin()..mergeFromMessage(this);
+  DartMixin clone() => deepCopy();
   @$core.Deprecated('Using this can add significant overhead to your binary. '
       'Use [GeneratedMessageGenericExtensions.rebuild] instead. '
       'Will be removed in next major version')
@@ -131,7 +131,7 @@ class Imports extends $pb.GeneratedMessage {
   @$core.Deprecated('Using this can add significant overhead to your binary. '
       'Use [GeneratedMessageGenericExtensions.deepCopy] instead. '
       'Will be removed in next major version')
-  Imports clone() => Imports()..mergeFromMessage(this);
+  Imports clone() => deepCopy();
   @$core.Deprecated('Using this can add significant overhead to your binary. '
       'Use [GeneratedMessageGenericExtensions.rebuild] instead. '
       'Will be removed in next major version')
diff --git a/protoc_plugin/lib/src/generated/descriptor.pb.dart b/protoc_plugin/lib/src/generated/descriptor.pb.dart
index f1afdbafe..ebee2c2e9 100644
--- a/protoc_plugin/lib/src/generated/descriptor.pb.dart
+++ b/protoc_plugin/lib/src/generated/descriptor.pb.dart
@@ -43,7 +43,7 @@ class FileDescriptorSet extends $pb.GeneratedMessage {
   @$core.Deprecated('Using this can add significant overhead to your binary. '
       'Use [GeneratedMessageGenericExtensions.deepCopy] instead. '
       'Will be removed in next major version')
-  FileDescriptorSet clone() => FileDescriptorSet()..mergeFromMessage(this);
+  FileDescriptorSet clone() => deepCopy();
   @$core.Deprecated('Using this can add significant overhead to your binary. '
       'Use [GeneratedMessageGenericExtensions.rebuild] instead. '
       'Will be removed in next major version')
@@ -159,7 +159,7 @@ class FileDescriptorProto extends $pb.GeneratedMessage {
   @$core.Deprecated('Using this can add significant overhead to your binary. '
       'Use [GeneratedMessageGenericExtensions.deepCopy] instead. '
       'Will be removed in next major version')
-  FileDescriptorProto clone() => FileDescriptorProto()..mergeFromMessage(this);
+  FileDescriptorProto clone() => deepCopy();
   @$core.Deprecated('Using this can add significant overhead to your binary. '
       'Use [GeneratedMessageGenericExtensions.rebuild] instead. '
       'Will be removed in next major version')
@@ -303,8 +303,7 @@ class DescriptorProto_ExtensionRange extends $pb.GeneratedMessage {
   @$core.Deprecated('Using this can add significant overhead to your binary. '
       'Use [GeneratedMessageGenericExtensions.deepCopy] instead. '
       'Will be removed in next major version')
-  DescriptorProto_ExtensionRange clone() =>
-      DescriptorProto_ExtensionRange()..mergeFromMessage(this);
+  DescriptorProto_ExtensionRange clone() => deepCopy();
   @$core.Deprecated('Using this can add significant overhead to your binary. '
       'Use [GeneratedMessageGenericExtensions.rebuild] instead. '
       'Will be removed in next major version')
@@ -399,8 +398,7 @@ class DescriptorProto_ReservedRange extends $pb.GeneratedMessage {
   @$core.Deprecated('Using this can add significant overhead to your binary. '
       'Use [GeneratedMessageGenericExtensions.deepCopy] instead. '
       'Will be removed in next major version')
-  DescriptorProto_ReservedRange clone() =>
-      DescriptorProto_ReservedRange()..mergeFromMessage(this);
+  DescriptorProto_ReservedRange clone() => deepCopy();
   @$core.Deprecated('Using this can add significant overhead to your binary. '
       'Use [GeneratedMessageGenericExtensions.rebuild] instead. '
       'Will be removed in next major version')
@@ -533,7 +531,7 @@ class DescriptorProto extends $pb.GeneratedMessage {
   @$core.Deprecated('Using this can add significant overhead to your binary. '
       'Use [GeneratedMessageGenericExtensions.deepCopy] instead. '
       'Will be removed in next major version')
-  DescriptorProto clone() => DescriptorProto()..mergeFromMessage(this);
+  DescriptorProto clone() => deepCopy();
   @$core.Deprecated('Using this can add significant overhead to your binary. '
       'Use [GeneratedMessageGenericExtensions.rebuild] instead. '
       'Will be removed in next major version')
@@ -632,8 +630,7 @@ class ExtensionRangeOptions extends $pb.GeneratedMessage {
   @$core.Deprecated('Using this can add significant overhead to your binary. '
       'Use [GeneratedMessageGenericExtensions.deepCopy] instead. '
       'Will be removed in next major version')
-  ExtensionRangeOptions clone() =>
-      ExtensionRangeOptions()..mergeFromMessage(this);
+  ExtensionRangeOptions clone() => deepCopy();
   @$core.Deprecated('Using this can add significant overhead to your binary. '
       'Use [GeneratedMessageGenericExtensions.rebuild] instead. '
       'Will be removed in next major version')
@@ -744,8 +741,7 @@ class FieldDescriptorProto extends $pb.GeneratedMessage {
   @$core.Deprecated('Using this can add significant overhead to your binary. '
       'Use [GeneratedMessageGenericExtensions.deepCopy] instead. '
       'Will be removed in next major version')
-  FieldDescriptorProto clone() =>
-      FieldDescriptorProto()..mergeFromMessage(this);
+  FieldDescriptorProto clone() => deepCopy();
   @$core.Deprecated('Using this can add significant overhead to your binary. '
       'Use [GeneratedMessageGenericExtensions.rebuild] instead. '
       'Will be removed in next major version')
@@ -931,8 +927,7 @@ class OneofDescriptorProto extends $pb.GeneratedMessage {
   @$core.Deprecated('Using this can add significant overhead to your binary. '
       'Use [GeneratedMessageGenericExtensions.deepCopy] instead. '
       'Will be removed in next major version')
-  OneofDescriptorProto clone() =>
-      OneofDescriptorProto()..mergeFromMessage(this);
+  OneofDescriptorProto clone() => deepCopy();
   @$core.Deprecated('Using this can add significant overhead to your binary. '
       'Use [GeneratedMessageGenericExtensions.rebuild] instead. '
       'Will be removed in next major version')
@@ -1013,8 +1008,7 @@ class EnumDescriptorProto_EnumReservedRange extends $pb.GeneratedMessage {
   @$core.Deprecated('Using this can add significant overhead to your binary. '
       'Use [GeneratedMessageGenericExtensions.deepCopy] instead. '
       'Will be removed in next major version')
-  EnumDescriptorProto_EnumReservedRange clone() =>
-      EnumDescriptorProto_EnumReservedRange()..mergeFromMessage(this);
+  EnumDescriptorProto_EnumReservedRange clone() => deepCopy();
   @$core.Deprecated('Using this can add significant overhead to your binary. '
       'Use [GeneratedMessageGenericExtensions.rebuild] instead. '
       'Will be removed in next major version')
@@ -1113,7 +1107,7 @@ class EnumDescriptorProto extends $pb.GeneratedMessage {
   @$core.Deprecated('Using this can add significant overhead to your binary. '
       'Use [GeneratedMessageGenericExtensions.deepCopy] instead. '
       'Will be removed in next major version')
-  EnumDescriptorProto clone() => EnumDescriptorProto()..mergeFromMessage(this);
+  EnumDescriptorProto clone() => deepCopy();
   @$core.Deprecated('Using this can add significant overhead to your binary. '
       'Use [GeneratedMessageGenericExtensions.rebuild] instead. '
       'Will be removed in next major version')
@@ -1207,8 +1201,7 @@ class EnumValueDescriptorProto extends $pb.GeneratedMessage {
   @$core.Deprecated('Using this can add significant overhead to your binary. '
       'Use [GeneratedMessageGenericExtensions.deepCopy] instead. '
       'Will be removed in next major version')
-  EnumValueDescriptorProto clone() =>
-      EnumValueDescriptorProto()..mergeFromMessage(this);
+  EnumValueDescriptorProto clone() => deepCopy();
   @$core.Deprecated('Using this can add significant overhead to your binary. '
       'Use [GeneratedMessageGenericExtensions.rebuild] instead. '
       'Will be removed in next major version')
@@ -1306,8 +1299,7 @@ class ServiceDescriptorProto extends $pb.GeneratedMessage {
   @$core.Deprecated('Using this can add significant overhead to your binary. '
       'Use [GeneratedMessageGenericExtensions.deepCopy] instead. '
       'Will be removed in next major version')
-  ServiceDescriptorProto clone() =>
-      ServiceDescriptorProto()..mergeFromMessage(this);
+  ServiceDescriptorProto clone() => deepCopy();
   @$core.Deprecated('Using this can add significant overhead to your binary. '
       'Use [GeneratedMessageGenericExtensions.rebuild] instead. '
       'Will be removed in next major version')
@@ -1409,8 +1401,7 @@ class MethodDescriptorProto extends $pb.GeneratedMessage {
   @$core.Deprecated('Using this can add significant overhead to your binary. '
       'Use [GeneratedMessageGenericExtensions.deepCopy] instead. '
       'Will be removed in next major version')
-  MethodDescriptorProto clone() =>
-      MethodDescriptorProto()..mergeFromMessage(this);
+  MethodDescriptorProto clone() => deepCopy();
   @$core.Deprecated('Using this can add significant overhead to your binary. '
       'Use [GeneratedMessageGenericExtensions.rebuild] instead. '
       'Will be removed in next major version')
@@ -1640,7 +1631,7 @@ class FileOptions extends $pb.GeneratedMessage {
   @$core.Deprecated('Using this can add significant overhead to your binary. '
       'Use [GeneratedMessageGenericExtensions.deepCopy] instead. '
       'Will be removed in next major version')
-  FileOptions clone() => FileOptions()..mergeFromMessage(this);
+  FileOptions clone() => deepCopy();
   @$core.Deprecated('Using this can add significant overhead to your binary. '
       'Use [GeneratedMessageGenericExtensions.rebuild] instead. '
       'Will be removed in next major version')
@@ -1955,7 +1946,7 @@ class MessageOptions extends $pb.GeneratedMessage {
   @$core.Deprecated('Using this can add significant overhead to your binary. '
       'Use [GeneratedMessageGenericExtensions.deepCopy] instead. '
       'Will be removed in next major version')
-  MessageOptions clone() => MessageOptions()..mergeFromMessage(this);
+  MessageOptions clone() => deepCopy();
   @$core.Deprecated('Using this can add significant overhead to your binary. '
       'Use [GeneratedMessageGenericExtensions.rebuild] instead. '
       'Will be removed in next major version')
@@ -2093,7 +2084,7 @@ class FieldOptions extends $pb.GeneratedMessage {
   @$core.Deprecated('Using this can add significant overhead to your binary. '
       'Use [GeneratedMessageGenericExtensions.deepCopy] instead. '
       'Will be removed in next major version')
-  FieldOptions clone() => FieldOptions()..mergeFromMessage(this);
+  FieldOptions clone() => deepCopy();
   @$core.Deprecated('Using this can add significant overhead to your binary. '
       'Use [GeneratedMessageGenericExtensions.rebuild] instead. '
       'Will be removed in next major version')
@@ -2217,7 +2208,7 @@ class OneofOptions extends $pb.GeneratedMessage {
   @$core.Deprecated('Using this can add significant overhead to your binary. '
       'Use [GeneratedMessageGenericExtensions.deepCopy] instead. '
       'Will be removed in next major version')
-  OneofOptions clone() => OneofOptions()..mergeFromMessage(this);
+  OneofOptions clone() => deepCopy();
   @$core.Deprecated('Using this can add significant overhead to your binary. '
       'Use [GeneratedMessageGenericExtensions.rebuild] instead. '
       'Will be removed in next major version')
@@ -2279,7 +2270,7 @@ class EnumOptions extends $pb.GeneratedMessage {
   @$core.Deprecated('Using this can add significant overhead to your binary. '
       'Use [GeneratedMessageGenericExtensions.deepCopy] instead. '
       'Will be removed in next major version')
-  EnumOptions clone() => EnumOptions()..mergeFromMessage(this);
+  EnumOptions clone() => deepCopy();
   @$core.Deprecated('Using this can add significant overhead to your binary. '
       'Use [GeneratedMessageGenericExtensions.rebuild] instead. '
       'Will be removed in next major version')
@@ -2359,7 +2350,7 @@ class EnumValueOptions extends $pb.GeneratedMessage {
   @$core.Deprecated('Using this can add significant overhead to your binary. '
       'Use [GeneratedMessageGenericExtensions.deepCopy] instead. '
       'Will be removed in next major version')
-  EnumValueOptions clone() => EnumValueOptions()..mergeFromMessage(this);
+  EnumValueOptions clone() => deepCopy();
   @$core.Deprecated('Using this can add significant overhead to your binary. '
       'Use [GeneratedMessageGenericExtensions.rebuild] instead. '
       'Will be removed in next major version')
@@ -2428,7 +2419,7 @@ class ServiceOptions extends $pb.GeneratedMessage {
   @$core.Deprecated('Using this can add significant overhead to your binary. '
       'Use [GeneratedMessageGenericExtensions.deepCopy] instead. '
       'Will be removed in next major version')
-  ServiceOptions clone() => ServiceOptions()..mergeFromMessage(this);
+  ServiceOptions clone() => deepCopy();
   @$core.Deprecated('Using this can add significant overhead to your binary. '
       'Use [GeneratedMessageGenericExtensions.rebuild] instead. '
       'Will be removed in next major version')
@@ -2506,7 +2497,7 @@ class MethodOptions extends $pb.GeneratedMessage {
   @$core.Deprecated('Using this can add significant overhead to your binary. '
       'Use [GeneratedMessageGenericExtensions.deepCopy] instead. '
       'Will be removed in next major version')
-  MethodOptions clone() => MethodOptions()..mergeFromMessage(this);
+  MethodOptions clone() => deepCopy();
   @$core.Deprecated('Using this can add significant overhead to your binary. '
       'Use [GeneratedMessageGenericExtensions.rebuild] instead. '
       'Will be removed in next major version')
@@ -2585,8 +2576,7 @@ class UninterpretedOption_NamePart extends $pb.GeneratedMessage {
   @$core.Deprecated('Using this can add significant overhead to your binary. '
       'Use [GeneratedMessageGenericExtensions.deepCopy] instead. '
       'Will be removed in next major version')
-  UninterpretedOption_NamePart clone() =>
-      UninterpretedOption_NamePart()..mergeFromMessage(this);
+  UninterpretedOption_NamePart clone() => deepCopy();
   @$core.Deprecated('Using this can add significant overhead to your binary. '
       'Use [GeneratedMessageGenericExtensions.rebuild] instead. '
       'Will be removed in next major version')
@@ -2695,7 +2685,7 @@ class UninterpretedOption extends $pb.GeneratedMessage {
   @$core.Deprecated('Using this can add significant overhead to your binary. '
       'Use [GeneratedMessageGenericExtensions.deepCopy] instead. '
       'Will be removed in next major version')
-  UninterpretedOption clone() => UninterpretedOption()..mergeFromMessage(this);
+  UninterpretedOption clone() => deepCopy();
   @$core.Deprecated('Using this can add significant overhead to your binary. '
       'Use [GeneratedMessageGenericExtensions.rebuild] instead. '
       'Will be removed in next major version')
@@ -2839,8 +2829,7 @@ class SourceCodeInfo_Location extends $pb.GeneratedMessage {
   @$core.Deprecated('Using this can add significant overhead to your binary. '
       'Use [GeneratedMessageGenericExtensions.deepCopy] instead. '
       'Will be removed in next major version')
-  SourceCodeInfo_Location clone() =>
-      SourceCodeInfo_Location()..mergeFromMessage(this);
+  SourceCodeInfo_Location clone() => deepCopy();
   @$core.Deprecated('Using this can add significant overhead to your binary. '
       'Use [GeneratedMessageGenericExtensions.rebuild] instead. '
       'Will be removed in next major version')
@@ -2923,7 +2912,7 @@ class SourceCodeInfo extends $pb.GeneratedMessage {
   @$core.Deprecated('Using this can add significant overhead to your binary. '
       'Use [GeneratedMessageGenericExtensions.deepCopy] instead. '
       'Will be removed in next major version')
-  SourceCodeInfo clone() => SourceCodeInfo()..mergeFromMessage(this);
+  SourceCodeInfo clone() => deepCopy();
   @$core.Deprecated('Using this can add significant overhead to your binary. '
       'Use [GeneratedMessageGenericExtensions.rebuild] instead. '
       'Will be removed in next major version')
@@ -2991,8 +2980,7 @@ class GeneratedCodeInfo_Annotation extends $pb.GeneratedMessage {
   @$core.Deprecated('Using this can add significant overhead to your binary. '
       'Use [GeneratedMessageGenericExtensions.deepCopy] instead. '
       'Will be removed in next major version')
-  GeneratedCodeInfo_Annotation clone() =>
-      GeneratedCodeInfo_Annotation()..mergeFromMessage(this);
+  GeneratedCodeInfo_Annotation clone() => deepCopy();
   @$core.Deprecated('Using this can add significant overhead to your binary. '
       'Use [GeneratedMessageGenericExtensions.rebuild] instead. '
       'Will be removed in next major version')
@@ -3083,7 +3071,7 @@ class GeneratedCodeInfo extends $pb.GeneratedMessage {
   @$core.Deprecated('Using this can add significant overhead to your binary. '
       'Use [GeneratedMessageGenericExtensions.deepCopy] instead. '
       'Will be removed in next major version')
-  GeneratedCodeInfo clone() => GeneratedCodeInfo()..mergeFromMessage(this);
+  GeneratedCodeInfo clone() => deepCopy();
   @$core.Deprecated('Using this can add significant overhead to your binary. '
       'Use [GeneratedMessageGenericExtensions.rebuild] instead. '
       'Will be removed in next major version')
diff --git a/protoc_plugin/lib/src/generated/plugin.pb.dart b/protoc_plugin/lib/src/generated/plugin.pb.dart
index 42e60cb89..f285091c6 100644
--- a/protoc_plugin/lib/src/generated/plugin.pb.dart
+++ b/protoc_plugin/lib/src/generated/plugin.pb.dart
@@ -60,7 +60,7 @@ class Version extends $pb.GeneratedMessage {
   @$core.Deprecated('Using this can add significant overhead to your binary. '
       'Use [GeneratedMessageGenericExtensions.deepCopy] instead. '
       'Will be removed in next major version')
-  Version clone() => Version()..mergeFromMessage(this);
+  Version clone() => deepCopy();
   @$core.Deprecated('Using this can add significant overhead to your binary. '
       'Use [GeneratedMessageGenericExtensions.rebuild] instead. '
       'Will be removed in next major version')
@@ -171,8 +171,7 @@ class CodeGeneratorRequest extends $pb.GeneratedMessage {
   @$core.Deprecated('Using this can add significant overhead to your binary. '
       'Use [GeneratedMessageGenericExtensions.deepCopy] instead. '
       'Will be removed in next major version')
-  CodeGeneratorRequest clone() =>
-      CodeGeneratorRequest()..mergeFromMessage(this);
+  CodeGeneratorRequest clone() => deepCopy();
   @$core.Deprecated('Using this can add significant overhead to your binary. '
       'Use [GeneratedMessageGenericExtensions.rebuild] instead. '
       'Will be removed in next major version')
@@ -267,8 +266,7 @@ class CodeGeneratorResponse_File extends $pb.GeneratedMessage {
   @$core.Deprecated('Using this can add significant overhead to your binary. '
       'Use [GeneratedMessageGenericExtensions.deepCopy] instead. '
       'Will be removed in next major version')
-  CodeGeneratorResponse_File clone() =>
-      CodeGeneratorResponse_File()..mergeFromMessage(this);
+  CodeGeneratorResponse_File clone() => deepCopy();
   @$core.Deprecated('Using this can add significant overhead to your binary. '
       'Use [GeneratedMessageGenericExtensions.rebuild] instead. '
       'Will be removed in next major version')
@@ -381,8 +379,7 @@ class CodeGeneratorResponse extends $pb.GeneratedMessage {
   @$core.Deprecated('Using this can add significant overhead to your binary. '
       'Use [GeneratedMessageGenericExtensions.deepCopy] instead. '
       'Will be removed in next major version')
-  CodeGeneratorResponse clone() =>
-      CodeGeneratorResponse()..mergeFromMessage(this);
+  CodeGeneratorResponse clone() => deepCopy();
   @$core.Deprecated('Using this can add significant overhead to your binary. '
       'Use [GeneratedMessageGenericExtensions.rebuild] instead. '
       'Will be removed in next major version')
diff --git a/protoc_plugin/lib/src/message_generator.dart b/protoc_plugin/lib/src/message_generator.dart
index cfbcdeec1..9cb3c7491 100644
--- a/protoc_plugin/lib/src/message_generator.dart
+++ b/protoc_plugin/lib/src/message_generator.dart
@@ -374,8 +374,7 @@ class MessageGenerator extends ProtobufContainer {
 'Using this can add significant overhead to your binary. '
 'Use [GeneratedMessageGenericExtensions.deepCopy] instead. '
 'Will be removed in next major version')''');
-      out.println('$classname clone() =>'
-          ' $classname()..mergeFromMessage(this);');
+      out.println('$classname clone() => deepCopy();');
       out.println('''@$coreImportPrefix.Deprecated(
 'Using this can add significant overhead to your binary. '
 'Use [GeneratedMessageGenericExtensions.rebuild] instead. '
diff --git a/protoc_plugin/test/goldens/grpc_service.pb b/protoc_plugin/test/goldens/grpc_service.pb
index 40d318a93..2731ef776 100644
--- a/protoc_plugin/test/goldens/grpc_service.pb
+++ b/protoc_plugin/test/goldens/grpc_service.pb
@@ -22,7 +22,7 @@ class Empty extends $pb.GeneratedMessage {
   'Using this can add significant overhead to your binary. '
   'Use [GeneratedMessageGenericExtensions.deepCopy] instead. '
   'Will be removed in next major version')
-  Empty clone() => Empty()..mergeFromMessage(this);
+  Empty clone() => deepCopy();
   @$core.Deprecated(
   'Using this can add significant overhead to your binary. '
   'Use [GeneratedMessageGenericExtensions.rebuild] instead. '
diff --git a/protoc_plugin/test/goldens/imports.pb b/protoc_plugin/test/goldens/imports.pb
index 51edcc115..aac9b6cfc 100644
--- a/protoc_plugin/test/goldens/imports.pb
+++ b/protoc_plugin/test/goldens/imports.pb
@@ -28,7 +28,7 @@ class M extends $pb.GeneratedMessage {
   'Using this can add significant overhead to your binary. '
   'Use [GeneratedMessageGenericExtensions.deepCopy] instead. '
   'Will be removed in next major version')
-  M clone() => M()..mergeFromMessage(this);
+  M clone() => deepCopy();
   @$core.Deprecated(
   'Using this can add significant overhead to your binary. '
   'Use [GeneratedMessageGenericExtensions.rebuild] instead. '
diff --git a/protoc_plugin/test/goldens/int64.pb b/protoc_plugin/test/goldens/int64.pb
index ce2101cc1..eb8af4d04 100644
--- a/protoc_plugin/test/goldens/int64.pb
+++ b/protoc_plugin/test/goldens/int64.pb
@@ -24,7 +24,7 @@ class Int64 extends $pb.GeneratedMessage {
   'Using this can add significant overhead to your binary. '
   'Use [GeneratedMessageGenericExtensions.deepCopy] instead. '
   'Will be removed in next major version')
-  Int64 clone() => Int64()..mergeFromMessage(this);
+  Int64 clone() => deepCopy();
   @$core.Deprecated(
   'Using this can add significant overhead to your binary. '
   'Use [GeneratedMessageGenericExtensions.rebuild] instead. '
diff --git a/protoc_plugin/test/goldens/messageGenerator b/protoc_plugin/test/goldens/messageGenerator
index 6840a22ff..8e9604154 100644
--- a/protoc_plugin/test/goldens/messageGenerator
+++ b/protoc_plugin/test/goldens/messageGenerator
@@ -14,7 +14,7 @@ class PhoneNumber extends $pb.GeneratedMessage {
   'Using this can add significant overhead to your binary. '
   'Use [GeneratedMessageGenericExtensions.deepCopy] instead. '
   'Will be removed in next major version')
-  PhoneNumber clone() => PhoneNumber()..mergeFromMessage(this);
+  PhoneNumber clone() => deepCopy();
   @$core.Deprecated(
   'Using this can add significant overhead to your binary. '
   'Use [GeneratedMessageGenericExtensions.rebuild] instead. '
diff --git a/protoc_plugin/test/goldens/messageGenerator.meta b/protoc_plugin/test/goldens/messageGenerator.meta
index e852febac..78e9c93c9 100644
--- a/protoc_plugin/test/goldens/messageGenerator.meta
+++ b/protoc_plugin/test/goldens/messageGenerator.meta
@@ -18,8 +18,8 @@ annotation: {
   path: 2
   path: 1
   sourceFile: 
-  begin: 2263
-  end: 2269
+  begin: 2236
+  end: 2242
 }
 annotation: {
   path: 4
@@ -27,8 +27,8 @@ annotation: {
   path: 2
   path: 1
   sourceFile: 
-  begin: 2311
-  end: 2317
+  begin: 2284
+  end: 2290
 }
 annotation: {
   path: 4
@@ -36,8 +36,8 @@ annotation: {
   path: 2
   path: 1
   sourceFile: 
-  begin: 2390
-  end: 2399
+  begin: 2363
+  end: 2372
 }
 annotation: {
   path: 4
@@ -45,8 +45,8 @@ annotation: {
   path: 2
   path: 1
   sourceFile: 
-  begin: 2442
-  end: 2453
+  begin: 2415
+  end: 2426
 }
 annotation: {
   path: 4
@@ -54,8 +54,8 @@ annotation: {
   path: 2
   path: 0
   sourceFile: 
-  begin: 2523
-  end: 2527
+  begin: 2496
+  end: 2500
 }
 annotation: {
   path: 4
@@ -63,8 +63,8 @@ annotation: {
   path: 2
   path: 0
   sourceFile: 
-  begin: 2568
-  end: 2572
+  begin: 2541
+  end: 2545
 }
 annotation: {
   path: 4
@@ -72,8 +72,8 @@ annotation: {
   path: 2
   path: 0
   sourceFile: 
-  begin: 2651
-  end: 2658
+  begin: 2624
+  end: 2631
 }
 annotation: {
   path: 4
@@ -81,8 +81,8 @@ annotation: {
   path: 2
   path: 0
   sourceFile: 
-  begin: 2701
-  end: 2710
+  begin: 2674
+  end: 2683
 }
 annotation: {
   path: 4
@@ -90,8 +90,8 @@ annotation: {
   path: 2
   path: 2
   sourceFile: 
-  begin: 2771
-  end: 2775
+  begin: 2744
+  end: 2748
 }
 annotation: {
   path: 4
@@ -99,8 +99,8 @@ annotation: {
   path: 2
   path: 2
   sourceFile: 
-  begin: 2822
-  end: 2826
+  begin: 2795
+  end: 2799
 }
 annotation: {
   path: 4
@@ -108,8 +108,8 @@ annotation: {
   path: 2
   path: 2
   sourceFile: 
-  begin: 2899
-  end: 2906
+  begin: 2872
+  end: 2879
 }
 annotation: {
   path: 4
@@ -117,8 +117,8 @@ annotation: {
   path: 2
   path: 2
   sourceFile: 
-  begin: 2949
-  end: 2958
+  begin: 2922
+  end: 2931
 }
 annotation: {
   path: 4
@@ -126,8 +126,8 @@ annotation: {
   path: 2
   path: 3
   sourceFile: 
-  begin: 3068
-  end: 3083
+  begin: 3041
+  end: 3056
 }
 annotation: {
   path: 4
@@ -135,8 +135,8 @@ annotation: {
   path: 2
   path: 3
   sourceFile: 
-  begin: 3174
-  end: 3189
+  begin: 3147
+  end: 3162
 }
 annotation: {
   path: 4
@@ -144,8 +144,8 @@ annotation: {
   path: 2
   path: 3
   sourceFile: 
-  begin: 3311
-  end: 3329
+  begin: 3284
+  end: 3302
 }
 annotation: {
   path: 4
@@ -153,6 +153,6 @@ annotation: {
   path: 2
   path: 3
   sourceFile: 
-  begin: 3421
-  end: 3441
+  begin: 3394
+  end: 3414
 }
diff --git a/protoc_plugin/test/goldens/oneMessage.pb b/protoc_plugin/test/goldens/oneMessage.pb
index 5c7885b2e..18921ae3a 100644
--- a/protoc_plugin/test/goldens/oneMessage.pb
+++ b/protoc_plugin/test/goldens/oneMessage.pb
@@ -24,7 +24,7 @@ class PhoneNumber extends $pb.GeneratedMessage {
   'Using this can add significant overhead to your binary. '
   'Use [GeneratedMessageGenericExtensions.deepCopy] instead. '
   'Will be removed in next major version')
-  PhoneNumber clone() => PhoneNumber()..mergeFromMessage(this);
+  PhoneNumber clone() => deepCopy();
   @$core.Deprecated(
   'Using this can add significant overhead to your binary. '
   'Use [GeneratedMessageGenericExtensions.rebuild] instead. '
diff --git a/protoc_plugin/test/goldens/oneMessage.pb.meta b/protoc_plugin/test/goldens/oneMessage.pb.meta
index 2dc041564..b9d529797 100644
--- a/protoc_plugin/test/goldens/oneMessage.pb.meta
+++ b/protoc_plugin/test/goldens/oneMessage.pb.meta
@@ -18,8 +18,8 @@ annotation: {
   path: 2
   path: 0
   sourceFile: test
-  begin: 2455
-  end: 2461
+  begin: 2428
+  end: 2434
 }
 annotation: {
   path: 4
@@ -27,8 +27,8 @@ annotation: {
   path: 2
   path: 0
   sourceFile: test
-  begin: 2503
-  end: 2509
+  begin: 2476
+  end: 2482
 }
 annotation: {
   path: 4
@@ -36,8 +36,8 @@ annotation: {
   path: 2
   path: 0
   sourceFile: test
-  begin: 2582
-  end: 2591
+  begin: 2555
+  end: 2564
 }
 annotation: {
   path: 4
@@ -45,8 +45,8 @@ annotation: {
   path: 2
   path: 0
   sourceFile: test
-  begin: 2634
-  end: 2645
+  begin: 2607
+  end: 2618
 }
 annotation: {
   path: 4
@@ -54,8 +54,8 @@ annotation: {
   path: 2
   path: 1
   sourceFile: test
-  begin: 2703
-  end: 2707
+  begin: 2676
+  end: 2680
 }
 annotation: {
   path: 4
@@ -63,8 +63,8 @@ annotation: {
   path: 2
   path: 1
   sourceFile: test
-  begin: 2749
-  end: 2753
+  begin: 2722
+  end: 2726
 }
 annotation: {
   path: 4
@@ -72,8 +72,8 @@ annotation: {
   path: 2
   path: 1
   sourceFile: test
-  begin: 2828
-  end: 2835
+  begin: 2801
+  end: 2808
 }
 annotation: {
   path: 4
@@ -81,8 +81,8 @@ annotation: {
   path: 2
   path: 1
   sourceFile: test
-  begin: 2878
-  end: 2887
+  begin: 2851
+  end: 2860
 }
 annotation: {
   path: 4
@@ -90,8 +90,8 @@ annotation: {
   path: 2
   path: 2
   sourceFile: test
-  begin: 2948
-  end: 2952
+  begin: 2921
+  end: 2925
 }
 annotation: {
   path: 4
@@ -99,8 +99,8 @@ annotation: {
   path: 2
   path: 2
   sourceFile: test
-  begin: 2999
-  end: 3003
+  begin: 2972
+  end: 2976
 }
 annotation: {
   path: 4
@@ -108,8 +108,8 @@ annotation: {
   path: 2
   path: 2
   sourceFile: test
-  begin: 3076
-  end: 3083
+  begin: 3049
+  end: 3056
 }
 annotation: {
   path: 4
@@ -117,6 +117,6 @@ annotation: {
   path: 2
   path: 2
   sourceFile: test
-  begin: 3126
-  end: 3135
+  begin: 3099
+  end: 3108
 }
diff --git a/protoc_plugin/test/goldens/service.pb b/protoc_plugin/test/goldens/service.pb
index ef803ecc5..5fa9749af 100644
--- a/protoc_plugin/test/goldens/service.pb
+++ b/protoc_plugin/test/goldens/service.pb
@@ -23,7 +23,7 @@ class Empty extends $pb.GeneratedMessage {
   'Using this can add significant overhead to your binary. '
   'Use [GeneratedMessageGenericExtensions.deepCopy] instead. '
   'Will be removed in next major version')
-  Empty clone() => Empty()..mergeFromMessage(this);
+  Empty clone() => deepCopy();
   @$core.Deprecated(
   'Using this can add significant overhead to your binary. '
   'Use [GeneratedMessageGenericExtensions.rebuild] instead. '