diff --git a/Changelog.md b/Changelog.md
index 5309e86b..9bbfcc52 100644
--- a/Changelog.md
+++ b/Changelog.md
@@ -6,6 +6,11 @@ Current master
 
 - Nothing yet!
 
+4.2.1
+-----
+
+- Add miminum platform requirements to Swift Package.
+
 4.2.0
 -----
 
diff --git a/Package.swift b/Package.swift
index 4e56afe7..cb9e61c4 100644
--- a/Package.swift
+++ b/Package.swift
@@ -4,6 +4,9 @@ import PackageDescription
 
 let package = Package(
     name: "Action",
+    platforms: [
+        .macOS(.v10_10), .iOS(.v8), .tvOS(.v9), .watchOS(.v3)
+    ],
     products: [
         // Products define the executables and libraries produced by a package, and make them visible to other packages.
         .library(