diff --git a/CHANGELOG.md b/CHANGELOG.md
index 89d51f7..2aa1857 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,10 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 ## [Unreleased]
+## [0.6.0] - 2019-09-02
+### Added
+- the `--retain-build` (`-b`) flag to retain the build number when bumping versions
+
 ## [0.5.0] - 2019-08-18
 ### Changed
 - the `bump build` command sets the subsequent numeric build parts to zeroes
@@ -41,7 +45,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Added
 - Initial version
 
-[Unreleased]: https://github.com/f3ath/pubspec-version/compare/0.5.0...HEAD
+[Unreleased]: https://github.com/f3ath/pubspec-version/compare/0.6.0...HEAD
+[0.6.0]: https://github.com/f3ath/pubspec-version/compare/0.5.0...0.6.0
 [0.5.0]: https://github.com/f3ath/pubspec-version/compare/0.4.0...0.5.0
 [0.4.0]: https://github.com/f3ath/pubspec-version/compare/0.3.0...0.4.0
 [0.3.0]: https://github.com/f3ath/pubspec-version/compare/0.2.2...0.3.0
diff --git a/bin/pubver.dart b/bin/pubver.dart
index 7daf311..d0b87eb 100644
--- a/bin/pubver.dart
+++ b/bin/pubver.dart
@@ -3,4 +3,4 @@ import 'dart:io';
 import 'package:pubspec_version/pubspec_version.dart';
 
 void main(List<String> args) async =>
-    exit(await Application(Console.stdio()).run(args));
+    exit((await buildApp(Console.stdio()).run(args)) ?? 0);
diff --git a/lib/pubspec_version.dart b/lib/pubspec_version.dart
index 0b385ed..06f13ea 100644
--- a/lib/pubspec_version.dart
+++ b/lib/pubspec_version.dart
@@ -1,2 +1,2 @@
-export 'package:pubspec_version/src/application.dart';
+export 'package:pubspec_version/src/cli/build_app.dart';
 export 'package:pubspec_version/src/console.dart';
diff --git a/lib/src/application.dart b/lib/src/application.dart
deleted file mode 100644
index 4908bff..0000000
--- a/lib/src/application.dart
+++ /dev/null
@@ -1,44 +0,0 @@
-import 'dart:async';
-
-import 'package:args/command_runner.dart';
-import 'package:pubspec_version/src/bump_version.dart';
-import 'package:pubspec_version/src/bumper.dart';
-import 'package:pubspec_version/src/console.dart';
-import 'package:pubspec_version/src/get_version_command.dart';
-import 'package:pubspec_version/src/next_build.dart';
-import 'package:pubspec_version/src/set_version_command.dart';
-
-class Application {
-  final Console console;
-
-  Application(this.console);
-
-  Future<int> run(List<String> args) async {
-    final bumpers = [
-      Bumper('breaking', 'Bumps the version to the next breaking.', console,
-          (_) => _.nextBreaking),
-      Bumper('major', 'Bumps the major version.', console, (_) => _.nextMajor),
-      Bumper('minor', 'Bumps the minor version.', console, (_) => _.nextMinor),
-      Bumper('patch', 'Bumps the patch version.', console, (_) => _.nextPatch),
-      Bumper('build', 'Bumps the first numeric part of the build version.',
-          console, nextBuild),
-    ];
-    final commandRunner =
-        await CommandRunner('pubver', 'Package version manager.')
-          ..addCommand(BumpVersionCommand(bumpers))
-          ..addCommand(SetVersionCommand(console))
-          ..addCommand(GetVersionCommand(console))
-          ..argParser.addOption('pubspec-dir',
-              abbr: 'd',
-              help: 'Directory containing pubspec.yaml.',
-              defaultsTo: '.');
-
-    try {
-      await commandRunner.run(args);
-      return 0;
-    } on UsageException catch (e) {
-      console.error(e.toString());
-      return 64;
-    }
-  }
-}
diff --git a/lib/src/bump_version.dart b/lib/src/bump_version.dart
deleted file mode 100644
index f9f3505..0000000
--- a/lib/src/bump_version.dart
+++ /dev/null
@@ -1,10 +0,0 @@
-import 'package:args/command_runner.dart';
-
-class BumpVersionCommand<T> extends Command<T> {
-  final name = 'bump';
-  final description = 'Bumps the package version.';
-
-  BumpVersionCommand(List<Command<T>> subcommands) {
-    subcommands.forEach(addSubcommand);
-  }
-}
diff --git a/lib/src/bumper.dart b/lib/src/bumper.dart
deleted file mode 100644
index c53ff9a..0000000
--- a/lib/src/bumper.dart
+++ /dev/null
@@ -1,16 +0,0 @@
-import 'package:pub_semver/pub_semver.dart';
-import 'package:pubspec_version/src/version_command.dart';
-
-import 'console.dart';
-
-class Bumper extends VersionCommand {
-  final String name;
-  final String description;
-  final _Mutator mutator;
-
-  Bumper(this.name, this.description, Console c, this.mutator) : super(c);
-
-  Version nextVersion(Version v) => mutator(v);
-}
-
-typedef Version _Mutator(Version v);
diff --git a/lib/src/cli/build_app.dart b/lib/src/cli/build_app.dart
new file mode 100644
index 0000000..be87b33
--- /dev/null
+++ b/lib/src/cli/build_app.dart
@@ -0,0 +1,88 @@
+import 'package:args/command_runner.dart';
+import 'package:pubspec_version/src/cli/command_container.dart';
+import 'package:pubspec_version/src/cli/pub_spec_command.dart';
+import 'package:pubspec_version/src/console.dart';
+
+CommandRunner<int> buildApp(Console console) =>
+    CommandRunner<int>('pubver', 'Package version manager.')
+      ..addCommand(CommandContainer(
+        'bump',
+        'Bumps the package version.',
+        [
+          PubSpecCommand(
+            'breaking',
+            'Bumps the version to the next breaking.',
+            (_) async {
+              await _.bumpBreaking();
+              console.log(await _.readVersion());
+              return 0;
+            },
+          ),
+          PubSpecCommand(
+            'major',
+            'Bumps the major version.',
+            (_) async {
+              await _.bumpMajor();
+              console.log(await _.readVersion());
+              return 0;
+            },
+          ),
+          PubSpecCommand(
+            'minor',
+            'Bumps the minor version.',
+            (_) async {
+              await _.bumpMinor();
+              console.log(await _.readVersion());
+              return 0;
+            },
+          ),
+          PubSpecCommand(
+            'patch',
+            'Bumps the patch version.',
+            (_) async {
+              await _.bumpPatch();
+              console.log(await _.readVersion());
+              return 0;
+            },
+          ),
+          PubSpecCommand(
+            'build',
+            'Bumps the first numeric part of the build version.',
+            (_) async {
+              await _.bumpBuild();
+              console.log(await _.readVersion());
+              return 0;
+            },
+          ),
+        ],
+      ))
+      ..addCommand(PubSpecCommand(
+        'set',
+        'Sets the package version.',
+        (_) async {
+          if (_.arguments.length < 2) {
+            console.error(
+                'Please provide the version' + '\n' * 2 + 'Example: set 3.2.1');
+            return 64;
+          }
+          await _.writeVersion(_.getArgument(1));
+          console.log(await _.readVersion());
+          return 0;
+        },
+      ))
+      ..addCommand(PubSpecCommand(
+        'get',
+        'Gets the current package version.',
+        (_) async {
+          console.log(await _.readVersion());
+          return 0;
+        },
+      ))
+      ..argParser.addOption('pubspec-dir',
+          abbr: 'd',
+          help: 'Directory containing pubspec.yaml.',
+          defaultsTo: '.')
+      ..argParser.addFlag('retain-build',
+          abbr: 'b',
+          help: 'Retain build when bumping major, minor, or patch.',
+          defaultsTo: false);
diff --git a/lib/src/cli/command_container.dart b/lib/src/cli/command_container.dart
new file mode 100644
index 0000000..d1a4f94
--- /dev/null
+++ b/lib/src/cli/command_container.dart
@@ -0,0 +1,10 @@
+import 'package:args/command_runner.dart';
+
+class CommandContainer<T> extends Command<T> {
+  final String name;
+  final String description;
+
+  CommandContainer(this.name, this.description, List<Command<T>> subcommands) {
+    subcommands.forEach(addSubcommand);
+  }
+}
diff --git a/lib/src/cli/pub_spec_command.dart b/lib/src/cli/pub_spec_command.dart
new file mode 100644
index 0000000..c743fa0
--- /dev/null
+++ b/lib/src/cli/pub_spec_command.dart
@@ -0,0 +1,36 @@
+import 'package:args/command_runner.dart';
+import 'package:pubspec_version/src/pubspec_version_app.dart';
+
+class PubSpecCommand extends Command<int> {
+  final String description;
+  final String name;
+  final _Payload _payload;
+
+  PubSpecCommand(this.name, this.description, this._payload);
+
+  bool get retainBuild => globalResults['retain-build'];
+
+  Future<String> readVersion() async => (await _app.readVersion()).toString();
+
+  Future<void> writeVersion(String version) => _app.writeVersionString(version);
+
+  Future<void> bumpBreaking() => _app.bumpBreaking(retainBuild: retainBuild);
+
+  Future<void> bumpMajor() => _app.bumpMajor(retainBuild: retainBuild);
+
+  Future<void> bumpMinor() => _app.bumpMinor(retainBuild: retainBuild);
+
+  Future<void> bumpPatch() => _app.bumpPatch(retainBuild: retainBuild);
+
+  Future<void> bumpBuild() => _app.bumpBuild();
+
+  String getArgument(int index) => globalResults.arguments[index];
+
+  List<String> get arguments => globalResults.arguments;
+
+  Future<int> run() => _payload(this);
+
+  PubSpecVersionApp get _app => PubSpecVersionApp(globalResults['pubspec-dir']);
+}
+
+typedef Future<int> _Payload(PubSpecCommand command);
diff --git a/lib/src/console.dart b/lib/src/console.dart
index 32e4524..112897e 100644
--- a/lib/src/console.dart
+++ b/lib/src/console.dart
@@ -12,8 +12,8 @@ class Console {
   Console.stdio() : this(stdout, stderr);
 
   /// Writes the [message] to the error sink
-  void error(Object message) => _error.writeln(message);
+  void error(Object message) => _error.writeln(message.toString());
 
   /// Writes the [message] the to the normal output sink
-  void log(Object message) => _output.writeln(message);
+  void log(Object message) => _output.writeln(message.toString());
 }
diff --git a/lib/src/get_version_command.dart b/lib/src/get_version_command.dart
deleted file mode 100644
index 091e6b1..0000000
--- a/lib/src/get_version_command.dart
+++ /dev/null
@@ -1,21 +0,0 @@
-import 'dart:async';
-import 'dart:io';
-
-import 'package:args/command_runner.dart';
-import 'package:pubspec/pubspec.dart';
-import 'package:pubspec_version/src/console.dart';
-
-class GetVersionCommand extends Command {
-  final Console console;
-  final name = 'get';
-  final description = 'Gets the current package version.';
-
-  GetVersionCommand(this.console);
-
-  @override
-  Future run() async {
-    final dir = Directory(globalResults['pubspec-dir']);
-    final pubSpec = await PubSpec.load(dir);
-    console.log(pubSpec.version.toString());
-  }
-}
diff --git a/lib/src/pubspec_version_app.dart b/lib/src/pubspec_version_app.dart
new file mode 100644
index 0000000..1795e36
--- /dev/null
+++ b/lib/src/pubspec_version_app.dart
@@ -0,0 +1,48 @@
+import 'dart:io';
+
+import 'package:pub_semver/pub_semver.dart';
+import 'package:pubspec/pubspec.dart' as ps;
+import 'package:pubspec_version/src/version_transform.dart';
+
+class PubSpecVersionApp {
+  final Directory _dir;
+
+  PubSpecVersionApp(String path) : _dir = Directory(path);
+
+  Future<VersionTransform> readVersion() async {
+    final pubSpec = await _load();
+    return VersionTransform(pubSpec.version);
+  }
+
+  Future<void> writeVersion(VersionTransform version) async {
+    final pubSpec = await _load();
+    await pubSpec.copy(version: version.version).save(_dir);
+  }
+
+  Future<void> writeVersionString(String version) =>
+      writeVersion(VersionTransform(Version.parse(version)));
+
+  Future<void> bumpBreaking({bool retainBuild = false}) =>
+      _update((_) => _.bumpBreaking(), retainBuild: retainBuild);
+
+  Future<void> bumpMajor({bool retainBuild = false}) =>
+      _update((_) => _.bumpMajor(), retainBuild: retainBuild);
+
+  Future<void> bumpMinor({bool retainBuild = false}) =>
+      _update((_) => _.bumpMinor(), retainBuild: retainBuild);
+
+  Future<void> bumpPatch({bool retainBuild = false}) =>
+      _update((_) => _.bumpPatch(), retainBuild: retainBuild);
+
+  Future<void> bumpBuild() => _update((_) => _.bumpBuild());
+
+  Future<void> _update(VersionTransform mutate(VersionTransform v),
+      {bool retainBuild = false}) async {
+    final version = await readVersion();
+    var newVersion =
+        retainBuild ? mutate(version).withBuildFrom(version) : mutate(version);
+    await writeVersion(newVersion);
+  }
+
+  Future<ps.PubSpec> _load() => ps.PubSpec.load(_dir);
+}
diff --git a/lib/src/set_version_command.dart b/lib/src/set_version_command.dart
deleted file mode 100644
index 2969711..0000000
--- a/lib/src/set_version_command.dart
+++ /dev/null
@@ -1,18 +0,0 @@
-import 'package:args/command_runner.dart';
-import 'package:pub_semver/pub_semver.dart';
-import 'package:pubspec_version/src/console.dart';
-import 'package:pubspec_version/src/version_command.dart';
-
-class SetVersionCommand extends VersionCommand {
-  final name = 'set';
-  final description = 'Sets the package version.';
-
-  SetVersionCommand(Console c) : super(c);
-
-  Version nextVersion(Version v) {
-    if (globalResults.arguments.length < 2) {
-      throw UsageException('Please provide the version', 'Example: set 3.2.1');
-    }
-    return Version.parse(globalResults.arguments[1]);
-  }
-}
diff --git a/lib/src/version_command.dart b/lib/src/version_command.dart
deleted file mode 100644
index c28fb7d..0000000
--- a/lib/src/version_command.dart
+++ /dev/null
@@ -1,23 +0,0 @@
-import 'dart:async';
-import 'dart:io';
-
-import 'package:args/command_runner.dart';
-import 'package:pub_semver/pub_semver.dart';
-import 'package:pubspec/pubspec.dart';
-import 'package:pubspec_version/src/console.dart';
-
-abstract class VersionCommand extends Command {
-  final Console console;
-
-  VersionCommand(this.console);
-
-  Future run() async {
-    final dir = Directory(globalResults['pubspec-dir']);
-    final pubSpec = await PubSpec.load(dir);
-    final version = nextVersion(pubSpec.version);
-    await pubSpec.copy(version: version).save(dir);
-    console.log(version.toString());
-  }
-
-  Version nextVersion(Version v);
-}
diff --git a/lib/src/version_transform.dart b/lib/src/version_transform.dart
new file mode 100644
index 0000000..07e8ebc
--- /dev/null
+++ b/lib/src/version_transform.dart
@@ -0,0 +1,37 @@
+import 'package:pub_semver/pub_semver.dart';
+
+class VersionTransform {
+  final Version version;
+
+  VersionTransform(this.version);
+
+  VersionTransform bumpBreaking() => VersionTransform(version.nextBreaking);
+
+  VersionTransform bumpMajor() => VersionTransform(version.nextMajor);
+
+  VersionTransform bumpMinor() => VersionTransform(version.nextMinor);
+
+  VersionTransform bumpPatch() => VersionTransform(version.nextPatch);
+
+  VersionTransform bumpBuild() {
+    var incremented = false;
+    final build = version.build.map((part) {
+      if (part is! int) return part;
+      if (incremented) return 0;
+      incremented = true;
+      return part + 1;
+    }).toList();
+    if (!incremented) build.add(1);
+    return withBuild(build);
+  }
+
+  VersionTransform withBuild(List build) =>
+      VersionTransform(Version(version.major, version.minor, version.patch,
+          build: build.join('.')));
+
+  VersionTransform withBuildFrom(VersionTransform other) =>
+      withBuild(other.version.build);
+
+  @override
+  String toString() => version.toString();
+}
diff --git a/test/functional_test.dart b/test/functional_test.dart
index fdcb75e..5bc376b 100644
--- a/test/functional_test.dart
+++ b/test/functional_test.dart
@@ -1,5 +1,6 @@
 import 'dart:io';
 
+import 'package:args/command_runner.dart';
 import 'package:mockito/mockito.dart';
 import 'package:pubspec/pubspec.dart';
 import 'package:pubspec_version/pubspec_version.dart';
@@ -10,18 +11,20 @@ class MockConsole extends Mock implements Console {}
 void main() {
   Directory temp;
   MockConsole mockConsole;
-  Application app;
+  CommandRunner<int> app;
 
   expectVersion(String v) async {
     expect((await PubSpec.load(Directory(temp.path))).version.toString(), v);
-    expect(verify(mockConsole.log(captureAny)).captured, [v]);
+    expect(
+        verify(mockConsole.log(captureAny)).captured.map((_) => _.toString()),
+        [v]);
   }
 
   setUp(() async {
     temp = await Directory.systemTemp.createTemp();
     File('test/pubspec_sample.yaml').copy('${temp.path}/pubspec.yaml');
     mockConsole = MockConsole();
-    app = Application(mockConsole);
+    app = buildApp(mockConsole);
   });
 
   tearDown(() async {
@@ -34,24 +37,48 @@ void main() {
     await expectVersion('0.4.0');
   });
 
+  test('bump breaking retaining build', () async {
+    final code = await app.run(['bump', 'breaking', '-d', temp.path, '-b']);
+    expect(code, 0);
+    await expectVersion('0.4.0+42');
+  });
+
   test('bump major', () async {
     final code = await app.run(['bump', 'major', '-d', temp.path]);
     expect(code, 0);
     await expectVersion('1.0.0');
   });
 
+  test('bump major retaining build', () async {
+    final code = await app.run(['bump', 'major', '-d', temp.path, '-b']);
+    expect(code, 0);
+    await expectVersion('1.0.0+42');
+  });
+
   test('bump minor', () async {
     final code = await app.run(['bump', 'minor', '-d', temp.path]);
     expect(code, 0);
     await expectVersion('0.4.0');
   });
 
+  test('bump minor retaining build', () async {
+    final code = await app.run(['bump', 'minor', '-d', temp.path, '-b']);
+    expect(code, 0);
+    await expectVersion('0.4.0+42');
+  });
+
   test('bump patch', () async {
     final code = await app.run(['bump', 'patch', '-d', temp.path]);
     expect(code, 0);
     await expectVersion('0.3.3');
   });
 
+  test('bump patch retaining build', () async {
+    final code = await app.run(['bump', 'patch', '-d', temp.path, '-b']);
+    expect(code, 0);
+    await expectVersion('0.3.3+42');
+  });
+
   test('bump build', () async {
     final code = await app.run(['bump', 'build', '-d', temp.path]);
     expect(code, 0);
diff --git a/test/unit/next_build_test.dart b/test/unit/version_transform_test.dart
similarity index 61%
rename from test/unit/next_build_test.dart
rename to test/unit/version_transform_test.dart
index d0a9a2f..bdc0a06 100644
--- a/test/unit/next_build_test.dart
+++ b/test/unit/version_transform_test.dart
@@ -1,20 +1,20 @@
 import 'package:pub_semver/pub_semver.dart';
-import 'package:pubspec_version/src/next_build.dart';
+import 'package:pubspec_version/src/version_transform.dart';
 import 'package:test/test.dart';
 
 void main() {
   test('bumping empty build sets it to 1', () async {
     final v = Version.parse('1.2.3');
-    expect(nextBuild(v).toString(), '1.2.3+1');
+    expect(VersionTransform(v).bumpBuild().toString(), '1.2.3+1');
   });
 
   test('non-numeric build gets ".1" appended to it', () async {
     final v = Version.parse('1.2.3+foo42');
-    expect(nextBuild(v).toString(), '1.2.3+foo42.1');
+    expect(VersionTransform(v).bumpBuild().toString(), '1.2.3+foo42.1');
   });
 
   test('in a complex build the first numeric part gets incremented', () async {
     final v = Version.parse('1.2.3+foo.1.2.3.bar');
-    expect(nextBuild(v).toString(), '1.2.3+foo.2.0.0.bar');
+    expect(VersionTransform(v).bumpBuild().toString(), '1.2.3+foo.2.0.0.bar');
   });
 }