diff --git a/Package.swift b/Package.swift
index f730f69..f60e023 100644
--- a/Package.swift
+++ b/Package.swift
@@ -1,11 +1,11 @@
-// swift-tools-version:5.0
+// swift-tools-version:6.0
 
 import PackageDescription
 
 let package = Package(
   name: "Then",
   platforms: [
-    .macOS(.v10_10), .iOS(.v9), .tvOS(.v9), .watchOS(.v2),
+    .macOS(.v10_13), .iOS(.v12), .tvOS(.v12), .watchOS(.v4),
   ],
   products: [
     .library(name: "Then", targets: ["Then"]),
diff --git a/Project.swift b/Project.swift
index 94d0723..e2cc816 100644
--- a/Project.swift
+++ b/Project.swift
@@ -24,7 +24,7 @@ let project = Project(
       headers: .headers(public: "Sources/Then/**/*.h"),
       settings: .settings(
         base: [
-          "SWIFT_VERSION": "5.0",
+          "SWIFT_VERSION": "6.0",
           "PRODUCT_NAME": "Then",
           "PRODUCT_MODULE_NAME": "Then",
         ],
@@ -43,7 +43,7 @@ let project = Project(
       ],
       settings: .settings(
         base: [
-          "SWIFT_VERSION": "5.0",
+          "SWIFT_VERSION": "6.0",
         ],
       ),
     ),
@@ -58,7 +58,7 @@ let project = Project(
       headers: .headers(public: "Sources/Then/**/*.h"),
       settings: .settings(
         base: [
-          "SWIFT_VERSION": "5.0",
+          "SWIFT_VERSION": "6.0",
           "PRODUCT_NAME": "Then",
           "PRODUCT_MODULE_NAME": "Then",
         ],
@@ -77,7 +77,7 @@ let project = Project(
       ],
       settings: .settings(
         base: [
-          "SWIFT_VERSION": "5.0",
+          "SWIFT_VERSION": "6.0",
         ],
       ),
     ),
@@ -92,7 +92,7 @@ let project = Project(
       headers: .headers(public: "Sources/Then/**/*.h"),
       settings: .settings(
         base: [
-          "SWIFT_VERSION": "5.0",
+          "SWIFT_VERSION": "6.0",
           "PRODUCT_NAME": "Then",
           "PRODUCT_MODULE_NAME": "Then",
         ],
@@ -111,7 +111,7 @@ let project = Project(
       ],
       settings: .settings(
         base: [
-          "SWIFT_VERSION": "5.0",
+          "SWIFT_VERSION": "6.0",
         ],
       ),
     ),
@@ -126,7 +126,7 @@ let project = Project(
       headers: .headers(public: "Sources/Then/**/*.h"),
       settings: .settings(
         base: [
-          "SWIFT_VERSION": "5.0",
+          "SWIFT_VERSION": "6.0",
           "PRODUCT_NAME": "Then",
           "PRODUCT_MODULE_NAME": "Then",
         ],
@@ -145,7 +145,7 @@ let project = Project(
       ],
       settings: .settings(
         base: [
-          "SWIFT_VERSION": "5.0",
+          "SWIFT_VERSION": "6.0",
         ],
       ),
     ),
diff --git a/Tests/ThenTests/ThenTests.swift b/Tests/ThenTests/ThenTests.swift
index 2fc7157..86ee6d0 100644
--- a/Tests/ThenTests/ThenTests.swift
+++ b/Tests/ThenTests/ThenTests.swift
@@ -70,4 +70,38 @@ class ThenTests: XCTestCase {
       },
     )
   }
+
+  @MainActor
+  func testThen_MainActorIsolated() {
+    @MainActor class MyView: NSObject {
+      var title: String = ""
+    }
+    let view = MyView().then {
+      $0.title = "hello"
+    }
+    XCTAssertEqual(view.title, "hello")
+  }
+
+  @MainActor
+  func testWith_MainActorIsolated() {
+    @MainActor struct Config: Then {
+      var value: Int = 0
+    }
+    let config = Config().with {
+      $0.value = 42
+    }
+    XCTAssertEqual(config.value, 42)
+  }
+
+  @MainActor
+  func testDo_MainActorIsolated() {
+    @MainActor class Store: NSObject {
+      var count: Int = 0
+    }
+    let store = Store()
+    store.do {
+      $0.count = 10
+    }
+    XCTAssertEqual(store.count, 10)
+  }
 }