diff --git a/Package.swift b/Package.swift
index 00ffeec..e5a5ce5 100644
--- a/Package.swift
+++ b/Package.swift
@@ -1,4 +1,4 @@
-// swift-tools-version:5.3
+// swift-tools-version:6.0
 // The swift-tools-version declares the minimum version of Swift required to build this package.
 
 import PackageDescription
diff --git a/Sources/SwiftUserDefaults/UserDefaults+Key.swift b/Sources/SwiftUserDefaults/UserDefaults+Key.swift
index 02796a4..3515772 100644
--- a/Sources/SwiftUserDefaults/UserDefaults+Key.swift
+++ b/Sources/SwiftUserDefaults/UserDefaults+Key.swift
@@ -65,7 +65,7 @@ public extension UserDefaults {
     ///
     /// let rawValue = UserDefaults.standard.string(forKey: UserDefaults.Key.userState.rawValue)
     /// ```
-    struct Key: RawRepresentable, Hashable {
+    struct Key: RawRepresentable, Hashable, Sendable {
         /// The underlying string value that is used for assigning a value against within the user defaults.
         public let rawValue: String
 
diff --git a/Sources/SwiftUserDefaults/UserDefaults+Observation.swift b/Sources/SwiftUserDefaults/UserDefaults+Observation.swift
index 139f75d..df6061e 100644
--- a/Sources/SwiftUserDefaults/UserDefaults+Observation.swift
+++ b/Sources/SwiftUserDefaults/UserDefaults+Observation.swift
@@ -22,8 +22,6 @@
 
 import Foundation
 
-private var userDefaultsObserverContext = 0
-
 public extension UserDefaults {
     /// Observes changes to the object associated with the specified key.
     ///
@@ -59,6 +57,7 @@ public extension UserDefaults {
         let userDefaults: UserDefaults
         let keyPath: String
         let handler: (Change<Any?>) -> Void
+        private var userDefaultsObserverContext = 0
 
         private(set) var isRegistered: Bool = false
 
diff --git a/Tests/SwiftUserDefaultsTests/UserDefaultTests.swift b/Tests/SwiftUserDefaultsTests/UserDefaultTests.swift
index 79513d9..6fc95d5 100644
--- a/Tests/SwiftUserDefaultsTests/UserDefaultTests.swift
+++ b/Tests/SwiftUserDefaultsTests/UserDefaultTests.swift
@@ -90,7 +90,6 @@ final class UserDefaultTests: XCTestCase {
 
         var changes: [UserDefaults.Change<String>] = []
         let observer = wrapper.addObserver { changes.append($0) }
-        addTeardownBlock(observer.invalidate)
 
         wrapper.wrappedValue = "One"
         wrapper.reset()
@@ -98,6 +97,7 @@ final class UserDefaultTests: XCTestCase {
         userDefaults.x.set("Three", forKey: .init("StringKey"))
 
         XCTAssertEqual(changes, [.initial(""), .update("One"), .update(""), .update("Two"), .update("Three")])
+        observer.invalidate()
     }
 
     func testCodableWithDefault() {
@@ -107,7 +107,6 @@ final class UserDefaultTests: XCTestCase {
         // Observe changes
         var changes: [Subject] = []
         let token = wrapper.addObserver(handler: { changes.append($0.value) })
-        addTeardownBlock(token.invalidate)
 
         // Uses default
         XCTAssertNil(userDefaults.object(forKey: key.rawValue))
@@ -133,6 +132,7 @@ final class UserDefaultTests: XCTestCase {
             "default",
             "default"
         ])
+        token.invalidate()
     }
 
     func testCodable() {
@@ -142,7 +142,6 @@ final class UserDefaultTests: XCTestCase {
         // Observe changes
         var changes: [Subject?] = []
         let token = wrapper.addObserver(handler: { changes.append($0.value) })
-        addTeardownBlock(token.invalidate)
 
         // nil when unset
         XCTAssertNil(userDefaults.object(forKey: key.rawValue))
@@ -175,6 +174,7 @@ final class UserDefaultTests: XCTestCase {
             "value",
             nil
         ])
+        token.invalidate()
     }
 
     func testRawRepresentableWithDefault() {
@@ -184,7 +184,6 @@ final class UserDefaultTests: XCTestCase {
         // Observe changes
         var changes: [RawSubject] = []
         let token = wrapper.addObserver(handler: { changes.append($0.value) })
-        addTeardownBlock(token.invalidate)
 
         // Uses default
         XCTAssertNil(userDefaults.object(forKey: key.rawValue))
@@ -210,6 +209,7 @@ final class UserDefaultTests: XCTestCase {
             .foo,
             .foo
         ])
+        token.invalidate()
     }
 
     func testRawRepresentable() {
@@ -219,7 +219,6 @@ final class UserDefaultTests: XCTestCase {
         // Observe changes
         var changes: [RawSubject?] = []
         let token = wrapper.addObserver(handler: { changes.append($0.value) })
-        addTeardownBlock(token.invalidate)
 
         // Uses default
         XCTAssertNil(userDefaults.object(forKey: key.rawValue))
@@ -251,5 +250,6 @@ final class UserDefaultTests: XCTestCase {
             nil,
             .baz
         ])
+        token.invalidate()
     }
 }
diff --git a/Tests/SwiftUserDefaultsTests/UserDefaultsObservationTests.swift b/Tests/SwiftUserDefaultsTests/UserDefaultsObservationTests.swift
index dedd3f2..c30610e 100644
--- a/Tests/SwiftUserDefaultsTests/UserDefaultsObservationTests.swift
+++ b/Tests/SwiftUserDefaultsTests/UserDefaultsObservationTests.swift
@@ -54,6 +54,27 @@ final class UserDefaultsObservationTests: XCTestCase {
         XCTAssertEqual(changes.map(\.value) as NSArray, [nil, "Test", nil, "Default", 1] as NSArray)
         XCTAssertEqual(changes.map(\.label), [.initial, .update, .update, .update, .update])
     }
+
+    func testInvalidateOnDeinit() {
+        // Given an observer is registered
+        var changes: [UserDefaults.Change<Any?>] = []
+
+        var observer: UserDefaults.Observation? = userDefaults.observeObject(forKey: "TestKey") { change in
+            changes.append(change)
+        }
+        _ = observer
+
+        userDefaults.set("Test", forKey: "TestKey")
+
+        // When the observer is deallocated
+        observer = nil
+
+        // Then no further changes should be recorded
+        userDefaults.set("NewTest", forKey: "TestKey")
+
+        XCTAssertEqual(changes.map(\.value) as NSArray, [nil, "Test"] as NSArray)
+        XCTAssertEqual(changes.map(\.label), [.initial, .update])
+    }
 }
 
 private extension UserDefaults.Change {