diff --git a/CHANGELOG.md b/CHANGELOG.md
index 80742fa..00b331b 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,7 +5,7 @@ All notable changes to this project are documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
-## [Unreleased]
+## [4.0.3] - 2026-08-22
 
 ### Added
 
@@ -126,7 +126,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - Initial release: Punycode (RFC 3492) encode/decode and IDNA encode/decode via `String` / `Substring` extensions.
 
-[Unreleased]: https://github.com/futamura/PunycodeSwift/compare/4.0.2...HEAD
+[Unreleased]: https://github.com/futamura/PunycodeSwift/compare/4.0.3...HEAD
+[4.0.3]: https://github.com/futamura/PunycodeSwift/compare/4.0.2...4.0.3
 [4.0.2]: https://github.com/futamura/PunycodeSwift/compare/4.0.1...4.0.2
 [4.0.1]: https://github.com/futamura/PunycodeSwift/compare/4.0.0...4.0.1
 [4.0.0]: https://github.com/futamura/PunycodeSwift/compare/3.0.0...4.0.0
diff --git a/Punycode.xcodeproj/project.pbxproj b/Punycode.xcodeproj/project.pbxproj
index 2d429f9..9b867a3 100644
--- a/Punycode.xcodeproj/project.pbxproj
+++ b/Punycode.xcodeproj/project.pbxproj
@@ -383,7 +383,7 @@
 					"@loader_path/Frameworks",
 				);
 				MACOSX_DEPLOYMENT_TARGET = 10.13;
-				MARKETING_VERSION = 4.0.2;
+				MARKETING_VERSION = 4.0.3;
 				MODULE_VERIFIER_SUPPORTED_LANGUAGES = "objective-c objective-c++";
 				MODULE_VERIFIER_SUPPORTED_LANGUAGE_STANDARDS = "gnu17 gnu++20";
 				PRODUCT_BUNDLE_IDENTIFIER = dev.futamura.Punycode;
@@ -429,7 +429,7 @@
 					"@loader_path/Frameworks",
 				);
 				MACOSX_DEPLOYMENT_TARGET = 10.13;
-				MARKETING_VERSION = 4.0.2;
+				MARKETING_VERSION = 4.0.3;
 				MODULE_VERIFIER_SUPPORTED_LANGUAGES = "objective-c objective-c++";
 				MODULE_VERIFIER_SUPPORTED_LANGUAGE_STANDARDS = "gnu17 gnu++20";
 				PRODUCT_BUNDLE_IDENTIFIER = dev.futamura.Punycode;
@@ -457,7 +457,7 @@
 				GENERATE_INFOPLIST_FILE = YES;
 				IPHONEOS_DEPLOYMENT_TARGET = 12.0;
 				MACOSX_DEPLOYMENT_TARGET = 10.13;
-				MARKETING_VERSION = 4.0.2;
+				MARKETING_VERSION = 4.0.3;
 				PRODUCT_BUNDLE_IDENTIFIER = dev.futamura.PunycodeTests;
 				PRODUCT_NAME = "$(TARGET_NAME)";
 				SDKROOT = auto;
@@ -481,7 +481,7 @@
 				GENERATE_INFOPLIST_FILE = YES;
 				IPHONEOS_DEPLOYMENT_TARGET = 12.0;
 				MACOSX_DEPLOYMENT_TARGET = 10.13;
-				MARKETING_VERSION = 4.0.2;
+				MARKETING_VERSION = 4.0.3;
 				PRODUCT_BUNDLE_IDENTIFIER = dev.futamura.PunycodeTests;
 				PRODUCT_NAME = "$(TARGET_NAME)";
 				SDKROOT = auto;