diff --git a/Example/SPM/FlexLayoutSample-SPM.xcodeproj/project.pbxproj b/Example/SPM/FlexLayoutSample-SPM.xcodeproj/project.pbxproj
index 3076c9a..2fb2c88 100644
--- a/Example/SPM/FlexLayoutSample-SPM.xcodeproj/project.pbxproj
+++ b/Example/SPM/FlexLayoutSample-SPM.xcodeproj/project.pbxproj
@@ -608,7 +608,7 @@
 					"$(inherited)",
 				);
 				INFOPLIST_FILE = "../FlexLayoutSample/Supporting Files/Info.plist";
-				IPHONEOS_DEPLOYMENT_TARGET = 12.0;
+				IPHONEOS_DEPLOYMENT_TARGET = 13.0;
 				LD_RUNPATH_SEARCH_PATHS = (
 					"$(inherited)",
 					"@executable_path/Frameworks",
@@ -631,7 +631,7 @@
 				CLANG_WARN_UNGUARDED_AVAILABILITY = YES_AGGRESSIVE;
 				CODE_SIGN_STYLE = Automatic;
 				INFOPLIST_FILE = "../FlexLayoutSample/Supporting Files/Info.plist";
-				IPHONEOS_DEPLOYMENT_TARGET = 12.0;
+				IPHONEOS_DEPLOYMENT_TARGET = 13.0;
 				LD_RUNPATH_SEARCH_PATHS = (
 					"$(inherited)",
 					"@executable_path/Frameworks",
diff --git a/Package.swift b/Package.swift
index 1c514ce..8c5f895 100644
--- a/Package.swift
+++ b/Package.swift
@@ -1,4 +1,4 @@
-// swift-tools-version:5.3
+// swift-tools-version:5.5
 // The swift-tools-version declares the minimum version of Swift required to build this package.
 
 import PackageDescription
@@ -6,7 +6,7 @@ import PackageDescription
 let package = Package(
   name: "FlexLayout",
   platforms: [
-    .iOS(.v12),
+    .iOS(.v13),
   ],
   products: [
     .library(name: "FlexLayout", targets: ["FlexLayout"]),
diff --git a/Podfile.lock b/Podfile.lock
index 3252b8f..9899cd7 100644
--- a/Podfile.lock
+++ b/Podfile.lock
@@ -1,5 +1,5 @@
 PODS:
-  - FlexLayout (2.2.0):
+  - FlexLayout (2.2.1):
     - Yoga (= 3.2.1)
   - PinLayout (1.10.5)
   - SwiftLint (0.55.1)
@@ -22,7 +22,7 @@ EXTERNAL SOURCES:
     :path: "./"
 
 SPEC CHECKSUMS:
-  FlexLayout: a8947ca2446760b5203ba5a3d862023c92a82fce
+  FlexLayout: fe365fe6e4a7bf1a53b7421a75acf4c7991e3575
   PinLayout: f6c2b63a5a5b24864064e1d15c67de41b4e74748
   SwiftLint: 3fe909719babe5537c552ee8181c0031392be933
   Yoga: 636ce73bd247407928a7df089f3bc3675916b3ff
diff --git a/README.md b/README.md
index fa70009..bb5d117 100644
--- a/README.md
+++ b/README.md
@@ -23,9 +23,9 @@ Flexbox is an incredible improvement over UIStackView. It is simpler to use, muc
 
 
 ### Requirements
-* iOS 12.0+
-* Xcode 12.0+
-* Swift Swift 4.0
+* iOS 13.0+
+* Xcode 13.0+
+* Swift 5.5
 
 ### Content
 
diff --git a/Sources/Swift/FlexLayout.swift b/Sources/Swift/FlexLayout.swift
index 211d31b..1d7782d 100644
--- a/Sources/Swift/FlexLayout.swift
+++ b/Sources/Swift/FlexLayout.swift
@@ -26,6 +26,7 @@ import FlexLayoutYogaKit
     label.flex.margin(10)
  ```
  */
+@MainActor
 public final class Flex {
     
     //
diff --git a/Sources/Swift/Impl/UIView+FlexLayout.swift b/Sources/Swift/Impl/UIView+FlexLayout.swift
index cb8ec2c..c617c17 100644
--- a/Sources/Swift/Impl/UIView+FlexLayout.swift
+++ b/Sources/Swift/Impl/UIView+FlexLayout.swift
@@ -14,6 +14,7 @@
 
 import UIKit
 
+@MainActor
 private var flexLayoutAssociatedObjectHandle = 72_399_923
 
 extension UIView {
diff --git a/Tests/FlexLayoutTests/FlexLayoutTests.swift b/Tests/FlexLayoutTests/FlexLayoutTests.swift
index 0b18c35..bb215a7 100644
--- a/Tests/FlexLayoutTests/FlexLayoutTests.swift
+++ b/Tests/FlexLayoutTests/FlexLayoutTests.swift
@@ -13,6 +13,7 @@
 import XCTest
 @testable import FlexLayout
 
+@MainActor
 final class FlexLayoutTests: XCTestCase {
 
     func testRetainCycle() {
diff --git a/Tests/FlexLayoutTests/InsetTests.swift b/Tests/FlexLayoutTests/InsetTests.swift
index 07591e3..a7bfb54 100644
--- a/Tests/FlexLayoutTests/InsetTests.swift
+++ b/Tests/FlexLayoutTests/InsetTests.swift
@@ -13,14 +13,15 @@
 import FlexLayout
 import XCTest
 
-final class InsetTests: XCTestCase {
+@MainActor
+final class InsetTests: XCTestCase, Sendable {
     
     var viewController: UIViewController!
     var rootFlexContainer: UIView!
     var aView: UIView!
     
-    override func setUp() {
-        super.setUp()
+    override func setUp() async throws {
+        try await super.setUp()
         
         viewController = UIViewController()
         
diff --git a/Tests/FlexLayoutTests/JustifyContentTests.swift b/Tests/FlexLayoutTests/JustifyContentTests.swift
index 4ff50d4..b98e119 100644
--- a/Tests/FlexLayoutTests/JustifyContentTests.swift
+++ b/Tests/FlexLayoutTests/JustifyContentTests.swift
@@ -13,7 +13,8 @@
 import FlexLayout
 import XCTest
 
-final class JustifyContentTests: XCTestCase {
+@MainActor
+final class JustifyContentTests: XCTestCase, Sendable {
 
     var viewController: UIViewController!
     var rootFlexContainer: UIView!
@@ -22,8 +23,8 @@ final class JustifyContentTests: XCTestCase {
     var cView: UIView!
     var dView: UIView!
 
-    override func setUp() {
-        super.setUp()
+    override func setUp() async throws {
+        try await super.setUp()
 
         viewController = UIViewController()
 
diff --git a/Tests/FlexLayoutTests/MarginTests.swift b/Tests/FlexLayoutTests/MarginTests.swift
index af4c497..3f0fc72 100644
--- a/Tests/FlexLayoutTests/MarginTests.swift
+++ b/Tests/FlexLayoutTests/MarginTests.swift
@@ -13,14 +13,15 @@
 import FlexLayout
 import XCTest
 
-final class MarginTests: XCTestCase {
+@MainActor
+final class MarginTests: XCTestCase, Sendable {
 
     var viewController: UIViewController!
     var rootFlexContainer: UIView!
     var aView: UIView!
 
-    override func setUp() {
-        super.setUp()
+    override func setUp() async throws {
+        try await super.setUp()
 
         viewController = UIViewController()
 
diff --git a/Tests/FlexLayoutTests/PaddingTests.swift b/Tests/FlexLayoutTests/PaddingTests.swift
index 0a76e4a..e43f775 100644
--- a/Tests/FlexLayoutTests/PaddingTests.swift
+++ b/Tests/FlexLayoutTests/PaddingTests.swift
@@ -13,14 +13,15 @@
 import FlexLayout
 import XCTest
 
-final class PaddingTests: XCTestCase {
+@MainActor
+final class PaddingTests: XCTestCase, Sendable {
 
     var viewController: UIViewController!
     var rootFlexContainer: UIView!
     var aView: UIView!
 
-    override func setUp() {
-        super.setUp()
+    override func setUp() async throws {
+        try await super.setUp()
 
         viewController = UIViewController()
 
diff --git a/Tests/FlexLayoutTests/WidthSizeContentTests.swift b/Tests/FlexLayoutTests/WidthSizeContentTests.swift
index 9baf2a7..d247e87 100644
--- a/Tests/FlexLayoutTests/WidthSizeContentTests.swift
+++ b/Tests/FlexLayoutTests/WidthSizeContentTests.swift
@@ -13,7 +13,8 @@
 import FlexLayout
 import XCTest
 
-final class WidthSizeContentTests: XCTestCase {
+@MainActor
+final class WidthSizeContentTests: XCTestCase, Sendable {
 
     var viewController: UIViewController!
     var rootFlexContainer: UIView!
@@ -21,8 +22,8 @@ final class WidthSizeContentTests: XCTestCase {
     var bView: UIView!
     var cView: UIView!
 
-    override func setUp() {
-        super.setUp()
+    override func setUp() async throws {
+        try await super.setUp()
 
         viewController = UIViewController()