diff --git a/Sources/Packages/Package.swift b/Sources/Packages/Package.swift
index 1594580..a666ec0 100644
--- a/Sources/Packages/Package.swift
+++ b/Sources/Packages/Package.swift
@@ -27,18 +27,26 @@ let package = Package(
         .library(
             name: "Brief",
             targets: ["Brief"]),
+        .library(
+            name: "Backports",
+            targets: ["Backports"]),
     ],
     dependencies: [
     ],
     targets: [
         .target(
-            name: "SecretKit",
+            name: "Backports",
             dependencies: [],
             swiftSettings: swiftSettings
         ),
+        .target(
+            name: "SecretKit",
+            dependencies: ["Backports"],
+            swiftSettings: swiftSettings
+        ),
         .testTarget(
             name: "SecretKitTests",
-            dependencies: ["SecretKit", "SecureEnclaveSecretKit", "SmartCardSecretKit"],
+            dependencies: ["Backports", "SecretKit", "SecureEnclaveSecretKit", "SmartCardSecretKit"],
             swiftSettings: swiftSettings
         ),
         .target(
@@ -48,12 +56,12 @@ let package = Package(
         ),
         .target(
             name: "SmartCardSecretKit",
-            dependencies: ["SecretKit"],
+            dependencies: ["Backports", "SecretKit"],
             swiftSettings: swiftSettings
         ),
         .target(
             name: "SecretAgentKit",
-            dependencies: ["SecretKit", "SecretAgentKitHeaders"],
+            dependencies: ["Backports", "SecretKit", "SecretAgentKitHeaders"],
             swiftSettings: swiftSettings
         ),
         .systemLibrary(
@@ -65,7 +73,7 @@ let package = Package(
         ,
         .target(
             name: "Brief",
-            dependencies: []
+            dependencies: ["Backports"]
         ),
         .testTarget(
             name: "BriefTests",
diff --git a/Sources/Packages/Sources/Backports/_Mutex.swift b/Sources/Packages/Sources/Backports/_Mutex.swift
new file mode 100644
index 0000000..b389a58
--- /dev/null
+++ b/Sources/Packages/Sources/Backports/_Mutex.swift
@@ -0,0 +1,30 @@
+import Foundation
+
+#if canImport(Synchronization)
+import Synchronization
+public typealias _Mutex = Mutex
+#else
+
+import os
+
+public final class _Mutex<Value: ~Copyable>: @unchecked Sendable {
+    
+    private var value: Value
+    private var lock = OSAllocatedUnfairLock()
+    
+    public init(_ value: consuming sending Value) {
+        self.value = value
+    }
+    
+    public borrowing func withLock<Result, E>(_ body: (inout sending Value) throws(E) -> sending Result) throws(E) -> sending Result where E : Error, Result : ~Copyable {
+        lock.lock()
+        defer {
+            lock.unlock()
+        }
+        return try body(&value)
+    }
+
+    
+}
+
+#endif
diff --git a/Sources/Packages/Sources/Brief/Updater.swift b/Sources/Packages/Sources/Brief/Updater.swift
index 334689d..315e779 100644
--- a/Sources/Packages/Sources/Brief/Updater.swift
+++ b/Sources/Packages/Sources/Brief/Updater.swift
@@ -1,6 +1,7 @@
 import Foundation
 import Observation
 import Synchronization
+import Backports
 
 /// A concrete implementation of ``UpdaterProtocol`` which considers the current release and OS version.
 @Observable public final class Updater: UpdaterProtocol, ObservableObject, Sendable {
@@ -8,7 +9,7 @@ import Synchronization
     public var update: Release? {
         _update.withLock { $0 }
     }
-    private let _update: Mutex<Release?> = .init(nil)
+    private let _update: _Mutex<Release?> = .init(nil)
     public let testBuild: Bool
 
     /// The current OS version.
diff --git a/Sources/Packages/Sources/SecretKit/OpenSSH/OpenSSHCertificateHandler.swift b/Sources/Packages/Sources/SecretKit/OpenSSH/OpenSSHCertificateHandler.swift
index d8345ba..fe0243c 100644
--- a/Sources/Packages/Sources/SecretKit/OpenSSH/OpenSSHCertificateHandler.swift
+++ b/Sources/Packages/Sources/SecretKit/OpenSSH/OpenSSHCertificateHandler.swift
@@ -1,6 +1,7 @@
 import Foundation
 import OSLog
 import Synchronization
+import Backports
 
 /// Manages storage and lookup for OpenSSH certificates.
 public final class OpenSSHCertificateHandler: Sendable {
@@ -8,7 +9,7 @@ public final class OpenSSHCertificateHandler: Sendable {
     private let publicKeyFileStoreController = PublicKeyFileStoreController(homeDirectory: NSHomeDirectory())
     private let logger = Logger(subsystem: "com.maxgoedjen.secretive.secretagent", category: "OpenSSHCertificateHandler")
     private let writer = OpenSSHKeyWriter()
-    private let keyBlobsAndNames: Mutex<[AnySecret: (Data, Data)]> = .init([:])
+    private let keyBlobsAndNames: _Mutex<[AnySecret: (Data, Data)]> = .init([:])
 
     /// Initializes an OpenSSHCertificateHandler.
     public init() {
diff --git a/Sources/Packages/Sources/SecretKit/SecretStoreList.swift b/Sources/Packages/Sources/SecretKit/SecretStoreList.swift
index b2ef3b2..be01ed5 100644
--- a/Sources/Packages/Sources/SecretKit/SecretStoreList.swift
+++ b/Sources/Packages/Sources/SecretKit/SecretStoreList.swift
@@ -1,6 +1,7 @@
 import Foundation
 import Observation
 import Synchronization
+import Backports
 
 /// A "Store Store," which holds a list of type-erased stores.
 @Observable public final class SecretStoreList: Sendable {
@@ -9,13 +10,13 @@ import Synchronization
     public var stores: [AnySecretStore] {
         __stores.withLock { $0 }
     }
-    private let __stores: Mutex<[AnySecretStore]> = .init([])
+    private let __stores: _Mutex<[AnySecretStore]> = .init([])
     
     /// A modifiable store, if one is available.
     public var modifiableStore: AnySecretStoreModifiable? {
         __modifiableStore.withLock { $0 }
     }
-    private let __modifiableStore: Mutex<AnySecretStoreModifiable?> = .init(nil)
+    private let __modifiableStore: _Mutex<AnySecretStoreModifiable?> = .init(nil)
 
     /// Initializes a SecretStoreList.
     public init() {
diff --git a/Sources/Packages/Sources/SecureEnclaveSecretKit/SecureEnclaveStore.swift b/Sources/Packages/Sources/SecureEnclaveSecretKit/SecureEnclaveStore.swift
index 371cdd5..c37b596 100644
--- a/Sources/Packages/Sources/SecureEnclaveSecretKit/SecureEnclaveStore.swift
+++ b/Sources/Packages/Sources/SecureEnclaveSecretKit/SecureEnclaveStore.swift
@@ -5,6 +5,7 @@ import CryptoKit
 import LocalAuthentication
 import SecretKit
 import Synchronization
+import Backports
 
 extension SecureEnclave {
 
@@ -19,9 +20,9 @@ extension SecureEnclave {
         public var secrets: [Secret] {
             _secrets.withLock { $0 }
         }
-        private let _secrets: Mutex<[Secret]> = .init([])
+        private let _secrets: _Mutex<[Secret]> = .init([])
 
-        private let persistedAuthenticationContexts: Mutex<[Secret: PersistentAuthenticationContext]> = .init([:])
+        private let persistedAuthenticationContexts: _Mutex<[Secret: PersistentAuthenticationContext]> = .init([:])
 
         /// Initializes a Store.
         public init() {
@@ -105,7 +106,7 @@ extension SecureEnclave {
         }
         
         public func sign(data: Data, with secret: Secret, for provenance: SigningRequestProvenance) throws -> Data {
-            let context: Mutex<LAContext>
+            let context: _Mutex<LAContext>
 //            if let existing = persistedAuthenticationContexts.withLock({ $0 })[secret], existing.valid {
 //                context = existing.context
 //            } else {
diff --git a/Sources/Packages/Sources/SmartCardSecretKit/SmartCardStore.swift b/Sources/Packages/Sources/SmartCardSecretKit/SmartCardStore.swift
index 199e4cd..d561605 100644
--- a/Sources/Packages/Sources/SmartCardSecretKit/SmartCardStore.swift
+++ b/Sources/Packages/Sources/SmartCardSecretKit/SmartCardStore.swift
@@ -5,6 +5,7 @@ import Security
 import CryptoTokenKit
 import LocalAuthentication
 import SecretKit
+import Backports
 
 extension SmartCard {
     
@@ -19,7 +20,7 @@ extension SmartCard {
     /// An implementation of Store backed by a Smart Card.
     @Observable public final class Store: SecretStore {
 
-        private let state: Mutex<State> = .init(.init())
+        private let state: _Mutex<State> = .init(.init())
         public var isAvailable: Bool {
             state.withLock { $0.isAvailable }
         }
diff --git a/Sources/SecretAgent/Notifier.swift b/Sources/SecretAgent/Notifier.swift
index 2f0e15a..ff1d147 100644
--- a/Sources/SecretAgent/Notifier.swift
+++ b/Sources/SecretAgent/Notifier.swift
@@ -5,6 +5,7 @@ import SecretKit
 import SecretAgentKit
 import Brief
 import Synchronization
+import Backports
 
 final class Notifier: Sendable {
 
@@ -151,7 +152,7 @@ final class NotificationDelegate: NSObject, UNUserNotificationCenterDelegate, Se
         fileprivate var pendingPersistableSecrets: [String: AnySecret] = [:]
     }
     
-    fileprivate let state: Mutex<State> = .init(.init())
+    fileprivate let state: _Mutex<State> = .init(.init())
     
     func userNotificationCenter(_ center: UNUserNotificationCenter, openSettingsFor notification: UNNotification?) {
 
diff --git a/Sources/Secretive/Preview Content/PreviewUpdater.swift b/Sources/Secretive/Preview Content/PreviewUpdater.swift
index 6979615..04c6658 100644
--- a/Sources/Secretive/Preview Content/PreviewUpdater.swift	
+++ b/Sources/Secretive/Preview Content/PreviewUpdater.swift	
@@ -2,13 +2,14 @@ import Foundation
 import Synchronization
 import Observation
 import Brief
+import Backports
 
 @Observable class PreviewUpdater: UpdaterProtocol {
 
     var update: Release? {
         _update.withLock { $0 }
     }
-    let _update: Mutex<Release?> = .init(nil)
+    let _update: _Mutex<Release?> = .init(nil)
 
     let testBuild = false