diff --git a/Sources/SWBUtil/AsyncLock.swift b/Sources/SWBUtil/AsyncLock.swift
index c2a5d5c6..5a7c3d34 100644
--- a/Sources/SWBUtil/AsyncLock.swift
+++ b/Sources/SWBUtil/AsyncLock.swift
@@ -18,7 +18,7 @@ public actor ActorLock {
     public init() {
     }
 
-    public func withLock<T: Sendable, E>(_ body: @Sendable () async throws(E) -> T) async throws(E) -> T {
+    public func withLock<T: Sendable, E>(_ body: sending () async throws(E) -> T) async throws(E) -> T {
         while busy {
             await withCheckedContinuation { cc in
                 queue.append(cc)
@@ -47,7 +47,7 @@ public final class AsyncLockedValue<Wrapped: Sendable> {
     }
 
     @discardableResult @inlinable
-    public func withLock<Result: Sendable, E>(_ block: @Sendable (inout Wrapped) async throws(E) -> Result) async throws(E) -> Result {
+    public func withLock<Result: Sendable, E>(_ block: sending (inout Wrapped) async throws(E) -> Result) async throws(E) -> Result {
         return try await lock.withLock { () throws(E) -> Result in try await block(&value) }
     }
 }
diff --git a/Sources/SWBUtil/HeavyCache.swift b/Sources/SWBUtil/HeavyCache.swift
index 190457e2..25cbd479 100644
--- a/Sources/SWBUtil/HeavyCache.swift
+++ b/Sources/SWBUtil/HeavyCache.swift
@@ -14,6 +14,8 @@
 import os
 #endif
 
+import Synchronization
+
 /// Base protocol used for global operations over generic type.
 private protocol _HeavyCacheBase: AnyObject {
     /// Clear the cache.
@@ -60,7 +62,7 @@ public func withHeavyCacheGlobalState<T>(isolated: Bool = true, _ body: () throw
 /// A cache designed for holding few, relatively heavy-weight objects.
 ///
 /// This cache is specifically designed for holding a limited number of objects (usually less than 100) which are expensive enough to merit particular attention in terms of being purgeable under memory pressure, evictable in-mass, or cached with more complex parameters like time-to-live (TTL).
-public final class HeavyCache<Key: Hashable, Value>: _HeavyCacheBase, KeyValueStorage, @unchecked Sendable {
+public final class HeavyCache<Key: Hashable & Sendable, Value>: _HeavyCacheBase, KeyValueStorage, @unchecked Sendable {
     public typealias HeavyCacheClock = SuspendingClock
 
     /// Controls the non-deterministic eviction policy of the cache. Note that this is distinct from deterministic _pruning_ (due to TTL or size limits).
@@ -86,7 +88,7 @@ public final class HeavyCache<Key: Hashable, Value>: _HeavyCacheBase, KeyValueSt
     }
 
     /// The lock to protect shared instance state.
-    private let stateLock = Lock()
+    private let stateLock = SWBMutex(())
 
     /// The underlying cache.
     private let _cache: any HeavyCacheImpl<Key, Entry>
diff --git a/Sources/SWBUtil/InterningArena.swift b/Sources/SWBUtil/InterningArena.swift
index c7f2c95e..11ca1435 100644
--- a/Sources/SWBUtil/InterningArena.swift
+++ b/Sources/SWBUtil/InterningArena.swift
@@ -18,7 +18,7 @@ public typealias FrozenStringArena = FrozenInterningArena<String>
 private let numberOfInternCalls = Statistic("InterningArena.numberOfInternCalls", "Number of calls to 'InterningArena.intern'")
 private let numberOfItemsInterned = Statistic("InterningArena.numberOfItemsInterned", "Number of items interned in InterningArenas")
 
-public final class InterningArena<T: Hashable> {
+public final class InterningArena<T: Hashable & Sendable> {
     public struct Handle: Hashable, Sendable {
         fileprivate let value: UInt32
 
diff --git a/Sources/SWBUtil/Lock.swift b/Sources/SWBUtil/Lock.swift
index d0334e6f..abc1664a 100644
--- a/Sources/SWBUtil/Lock.swift
+++ b/Sources/SWBUtil/Lock.swift
@@ -110,7 +110,7 @@ extension LockedValue where Value: ~Copyable {
 extension LockedValue: @unchecked Sendable where Value: ~Copyable {
 }
 
-extension LockedValue {
+extension LockedValue where Value: Sendable {
     /// Sets the value of the wrapped value to `newValue` and returns the original value.
     public func exchange(_ newValue: Value) -> Value {
         withLock {
diff --git a/Sources/SWBUtil/Statistics.swift b/Sources/SWBUtil/Statistics.swift
index 7f7eed87..7d9fd51b 100644
--- a/Sources/SWBUtil/Statistics.swift
+++ b/Sources/SWBUtil/Statistics.swift
@@ -115,7 +115,7 @@ public final class Statistic: @unchecked Sendable, _StatisticBackend {
     }
 }
 
-public protocol _StatisticBackend {
+public protocol _StatisticBackend: Sendable {
     var name: String { get }
     var value: Int { get }
     func increment(_ n: Int)