diff --git a/packages/freezed/CHANGELOG.md b/packages/freezed/CHANGELOG.md
index da139a99..7cc906e6 100644
--- a/packages/freezed/CHANGELOG.md
+++ b/packages/freezed/CHANGELOG.md
@@ -1,6 +1,7 @@
-## Unreleased minor
+## Unreleased patch
 
-Added `when`/`map` back
+- Added `when`/`map` back
+- Stop writing `// dart format width=80` to the generated freezed files.
 
 ## 3.0.6 - 2025-04-05
 
diff --git a/packages/freezed/lib/builder.dart b/packages/freezed/lib/builder.dart
index 535b5f88..1330bab7 100644
--- a/packages/freezed/lib/builder.dart
+++ b/packages/freezed/lib/builder.dart
@@ -1,5 +1,7 @@
 import 'package:build/build.dart';
+import 'package:dart_style/dart_style.dart' show DartFormatter;
 import 'package:freezed_annotation/freezed_annotation.dart';
+import 'package:pub_semver/pub_semver.dart' show Version;
 import 'package:source_gen/source_gen.dart';
 
 import 'src/freezed_generator.dart';
@@ -14,6 +16,7 @@ Builder freezed(BuilderOptions options) {
       ),
     ],
     '.freezed.dart',
+    formatOutput: _defaultFormatOutput,
     header: '''
 // coverage:ignore-file
 // GENERATED CODE - DO NOT MODIFY BY HAND
@@ -23,3 +26,6 @@ Builder freezed(BuilderOptions options) {
     options: options,
   );
 }
+
+String _defaultFormatOutput(String code, Version version) =>
+    DartFormatter(languageVersion: version).format(code);
diff --git a/packages/freezed/pubspec.yaml b/packages/freezed/pubspec.yaml
index 8b06f6ba..7a78a13f 100644
--- a/packages/freezed/pubspec.yaml
+++ b/packages/freezed/pubspec.yaml
@@ -18,6 +18,8 @@ dependencies:
   source_gen: ^2.0.0
   freezed_annotation: ^3.0.0
   json_annotation: ^4.8.0
+  dart_style: ^3.0.0
+  pub_semver: ^2.2.0
 
 dev_dependencies:
   json_serializable: ^6.3.2
diff --git a/packages/freezed/test/source_gen_test.dart b/packages/freezed/test/source_gen_test.dart
index b848ec8c..56bdd8d1 100644
--- a/packages/freezed/test/source_gen_test.dart
+++ b/packages/freezed/test/source_gen_test.dart
@@ -1,8 +1,10 @@
 import 'dart:async';
+import 'dart:io' show Directory, File;
 
 import 'package:freezed/src/freezed_generator.dart';
 import 'package:freezed_annotation/freezed_annotation.dart';
 import 'package:source_gen_test/source_gen_test.dart';
+import 'package:test/test.dart';
 
 Future<void> main() async {
   final reader = await initializeLibraryReaderForDirectory(
@@ -16,4 +18,37 @@ Future<void> main() async {
     reader,
     FreezedGenerator(Freezed.fromJson(<Object?, Object?>{}), format: false),
   );
+
+  test('generated files do not contain default source_gen header', () {
+    // Read generated files from the integration folder.
+    final generatedFiles = Directory('test/integration')
+        .listSync(recursive: true)
+        .whereType<File>()
+        .where((e) => e.path.endsWith('.freezed.dart'))
+        .toList();
+
+    // Ensure we have files to test
+    expect(
+      generatedFiles,
+      isNotEmpty,
+      reason: 'Expected to find .freezed.dart files in test/integration',
+    );
+
+    for (final file in generatedFiles) {
+      final content = file.readAsStringSync();
+
+      // Verify the custom header is present
+      expect(content, contains('// coverage:ignore-file'));
+      expect(content, contains('// GENERATED CODE - DO NOT MODIFY BY HAND'));
+      expect(content, contains('// ignore_for_file: type=lint'));
+
+      // Verify the default source_gen header is NOT present
+      expect(
+        content,
+        isNot(contains('// dart format width')),
+        reason:
+            'File ${file.path} should not contain default source_gen header',
+      );
+    }
+  });
 }