diff --git a/protobuf/lib/protobuf.dart b/protobuf/lib/protobuf.dart
index f68e779a..f2880196 100644
--- a/protobuf/lib/protobuf.dart
+++ b/protobuf/lib/protobuf.dart
@@ -18,7 +18,5 @@ export 'src/protobuf/internal.dart'
         GeneratedMessageInternalExtension,
         MapFieldInfoInternalExtension,
         checkNotNull,
-        mapKeyFieldNumber,
-        mapValueFieldNumber,
         mergeFromProto3JsonAny,
         writeToProto3JsonAny;
diff --git a/protobuf/lib/src/protobuf/coded_buffer.dart b/protobuf/lib/src/protobuf/coded_buffer.dart
index 2a97d51e..ebfe6d7c 100644
--- a/protobuf/lib/src/protobuf/coded_buffer.dart
+++ b/protobuf/lib/src/protobuf/coded_buffer.dart
@@ -355,15 +355,32 @@ void _mergeFromCodedBufferReader(
       case PbFieldType.MAP:
         final mapFieldInfo = fi as MapFieldInfo;
         final mapEntryMeta = mapFieldInfo.mapEntryBuilderInfo;
-        fs
-            ._ensureMapField(meta, mapFieldInfo)
-            ._mergeEntry(mapEntryMeta, input, registry);
+        final map = fs._ensureMapField(meta, mapFieldInfo);
+        _readMapEntry(map, mapEntryMeta, input, registry);
       default:
         throw UnsupportedError('Unknown field type $fieldType');
     }
   }
 }
 
+void _readMapEntry(
+  PbMap map,
+  BuilderInfo meta,
+  CodedBufferReader input,
+  ExtensionRegistry registry,
+) {
+  final length = input.readInt32();
+  final oldLimit = input._currentLimit;
+  input._currentLimit = input._bufferPos + length;
+  final entryFieldSet = FieldSet(null, meta);
+  _mergeFromCodedBufferReader(meta, entryFieldSet, input, registry);
+  input.checkLastTagWas(0);
+  input._currentLimit = oldLimit;
+  final key = entryFieldSet._values[0] ?? meta.byIndex[0].makeDefault!();
+  final value = entryFieldSet._values[1] ?? meta.byIndex[1].makeDefault!();
+  map[key] = value;
+}
+
 void _readPackableToListEnum(
   List list,
   BuilderInfo meta,
diff --git a/protobuf/lib/src/protobuf/coded_buffer_writer.dart b/protobuf/lib/src/protobuf/coded_buffer_writer.dart
index 8d0e198b..387fb2e2 100644
--- a/protobuf/lib/src/protobuf/coded_buffer_writer.dart
+++ b/protobuf/lib/src/protobuf/coded_buffer_writer.dart
@@ -88,14 +88,9 @@ class CodedBufferWriter {
       map.forEach((key, value) {
         _writeTag(fieldNumber, WIRETYPE_LENGTH_DELIMITED);
         final mark = _startLengthDelimited();
+        _writeValue(mapKeyFieldNumber, map.keyFieldType, key, keyWireFormat);
         _writeValue(
-          PbMap._keyFieldNumber,
-          map.keyFieldType,
-          key,
-          keyWireFormat,
-        );
-        _writeValue(
-          PbMap._valueFieldNumber,
+          mapValueFieldNumber,
           map.valueFieldType,
           value,
           valueWireFormat,
diff --git a/protobuf/lib/src/protobuf/extension_field_set.dart b/protobuf/lib/src/protobuf/extension_field_set.dart
index fc73fc30..bb954e25 100644
--- a/protobuf/lib/src/protobuf/extension_field_set.dart
+++ b/protobuf/lib/src/protobuf/extension_field_set.dart
@@ -232,7 +232,7 @@ class ExtensionFieldSet {
       final fieldInfo = _info[tag]!;
       if (fieldInfo.isMapField) {
         final PbMap? map = value;
-        newValues[tag] = map?._deepCopy();
+        newValues[tag] = map?.deepCopy();
       } else if (fieldInfo.isRepeated) {
         final PbList? list = value;
         newValues[tag] = list?.deepCopy();
diff --git a/protobuf/lib/src/protobuf/field_info.dart b/protobuf/lib/src/protobuf/field_info.dart
index dbdd7d0e..cf5b28cc 100644
--- a/protobuf/lib/src/protobuf/field_info.dart
+++ b/protobuf/lib/src/protobuf/field_info.dart
@@ -311,7 +311,7 @@ class MapFieldInfo<K, V> extends FieldInfo<PbMap<K, V>?> {
   }
 
   FieldInfo get valueFieldInfo =>
-      mapEntryBuilderInfo.fieldInfo[PbMap._valueFieldNumber]!;
+      mapEntryBuilderInfo.fieldInfo[mapValueFieldNumber]!;
 
   PbMap<K, V> _ensureMapField(BuilderInfo meta, FieldSet fs) {
     return fs._ensureMapField<K, V>(meta, this);
diff --git a/protobuf/lib/src/protobuf/field_set.dart b/protobuf/lib/src/protobuf/field_set.dart
index eb90a79b..e2f03f9e 100644
--- a/protobuf/lib/src/protobuf/field_set.dart
+++ b/protobuf/lib/src/protobuf/field_set.dart
@@ -953,7 +953,7 @@ class FieldSet {
       if (fieldInfo.isMapField) {
         final PbMap? originalMap = original._values[index];
         if (originalMap == null) continue;
-        _values[index] = originalMap._deepCopy();
+        _values[index] = originalMap.deepCopy();
       } else if (fieldInfo.isRepeated) {
         final PbList? originalList = original._values[index];
         if (originalList == null) continue;
diff --git a/protobuf/lib/src/protobuf/internal.dart b/protobuf/lib/src/protobuf/internal.dart
index f8e9eda7..4bfd34b0 100644
--- a/protobuf/lib/src/protobuf/internal.dart
+++ b/protobuf/lib/src/protobuf/internal.dart
@@ -7,7 +7,6 @@
 /// [1]: https://developers.google.com/protocol-buffers
 library;
 
-import 'dart:collection' show MapBase;
 import 'dart:convert' show Utf8Decoder, Utf8Encoder, base64Decode, base64Encode;
 import 'dart:math' as math;
 import 'dart:typed_data' show ByteData, Endian, Uint8List;
@@ -21,11 +20,13 @@ import 'json/json.dart' as json_lib;
 import 'json_parsing_context.dart';
 import 'mixins/well_known.dart';
 import 'pb_list.dart';
+import 'pb_map.dart';
 import 'permissive_compare.dart';
 import 'type_registry.dart';
 import 'utils.dart';
 
 export 'pb_list.dart' show PbList;
+export 'pb_map.dart' show PbMap;
 export 'type_registry.dart' show TypeRegistry;
 
 part 'annotations.dart';
@@ -44,7 +45,6 @@ part 'field_type.dart';
 part 'generated_message.dart';
 part 'generated_service.dart';
 part 'message_set.dart';
-part 'pb_map.dart';
 part 'proto3_json.dart';
 part 'protobuf_enum.dart';
 part 'rpc_client.dart';
diff --git a/protobuf/lib/src/protobuf/json/json.dart b/protobuf/lib/src/protobuf/json/json.dart
index 05d1ac11..84c87193 100644
--- a/protobuf/lib/src/protobuf/json/json.dart
+++ b/protobuf/lib/src/protobuf/json/json.dart
@@ -8,6 +8,7 @@ import 'package:fixnum/fixnum.dart' show Int64;
 
 import '../consts.dart';
 import '../internal.dart';
+import '../pb_map.dart';
 import '../utils.dart';
 
 // Use json_vm.dart with VM and dart2wasm, json_web.dart with dart2js.
diff --git a/protobuf/lib/src/protobuf/json/json_web.dart b/protobuf/lib/src/protobuf/json/json_web.dart
index 84d6482f..1912ffd4 100644
--- a/protobuf/lib/src/protobuf/json/json_web.dart
+++ b/protobuf/lib/src/protobuf/json/json_web.dart
@@ -10,6 +10,7 @@ import 'package:fixnum/fixnum.dart' show Int64;
 
 import '../consts.dart';
 import '../internal.dart';
+import '../pb_map.dart';
 import '../utils.dart';
 
 @JS('JSON')
diff --git a/protobuf/lib/src/protobuf/pb_map.dart b/protobuf/lib/src/protobuf/pb_map.dart
index 0f45c2cf..00513337 100644
--- a/protobuf/lib/src/protobuf/pb_map.dart
+++ b/protobuf/lib/src/protobuf/pb_map.dart
@@ -2,7 +2,10 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-part of 'internal.dart';
+import 'dart:collection' show MapBase;
+
+import 'internal.dart';
+import 'utils.dart';
 
 const mapKeyFieldNumber = 1;
 const mapValueFieldNumber = 2;
@@ -21,9 +24,6 @@ class PbMap<K, V> extends MapBase<K, V> {
   /// The `int` value is interpreted the same way as [FieldInfo.type].
   final int valueFieldType;
 
-  static const int _keyFieldNumber = 1;
-  static const int _valueFieldNumber = 2;
-
   /// The actual list storing the elements.
   ///
   /// Note: We want only one [Map] implementation class to be stored here to
@@ -103,25 +103,6 @@ class PbMap<K, V> extends MapBase<K, V> {
     return _wrappedMap.remove(key);
   }
 
-  void _mergeEntry(
-    BuilderInfo mapEntryMeta,
-    CodedBufferReader input,
-    ExtensionRegistry registry,
-  ) {
-    final length = input.readInt32();
-    final oldLimit = input._currentLimit;
-    input._currentLimit = input._bufferPos + length;
-    final entryFieldSet = FieldSet(null, mapEntryMeta);
-    _mergeFromCodedBufferReader(mapEntryMeta, entryFieldSet, input, registry);
-    input.checkLastTagWas(0);
-    input._currentLimit = oldLimit;
-    final key =
-        entryFieldSet._values[0] ?? mapEntryMeta.byIndex[0].makeDefault!();
-    final value =
-        entryFieldSet._values[1] ?? mapEntryMeta.byIndex[1].makeDefault!();
-    _wrappedMap[key] = value;
-  }
-
   PbMap freeze() {
     _isReadOnly = true;
     if (PbFieldType.isGroupOrMessage(valueFieldType)) {
@@ -147,3 +128,10 @@ class PbMap<K, V> extends MapBase<K, V> {
     return newMap;
   }
 }
+
+extension PbMapInternalExtension<K, V> on PbMap<K, V> {
+  @pragma('dart2js:tryInline')
+  @pragma('vm:prefer-inline')
+  @pragma('wasm:prefer-inline')
+  PbMap<K, V> deepCopy() => _deepCopy();
+}