diff --git a/Sources/HTTPTypes/HTTPFields.swift b/Sources/HTTPTypes/HTTPFields.swift
index df8a141..c368dc9 100644
--- a/Sources/HTTPTypes/HTTPFields.swift
+++ b/Sources/HTTPTypes/HTTPFields.swift
@@ -32,7 +32,7 @@ public struct HTTPFields: Sendable, Hashable {
         required init() {
         }
 
-        func withLock<Result>(_ body: () throws -> Result) rethrows -> Result {
+        func withLock<Result>(_ body: () throws -> sending Result) rethrows -> sending Result {
             fatalError()
         }
 
@@ -114,7 +114,7 @@ public struct HTTPFields: Sendable, Hashable {
     private final class _StorageWithMutex: _Storage, @unchecked Sendable {
         let mutex = Mutex<Void>(())
 
-        override func withLock<Result>(_ body: () throws -> Result) rethrows -> Result {
+        override func withLock<Result>(_ body: () throws -> sending Result) rethrows -> sending Result {
             try self.mutex.withLock { _ in
                 try body()
             }
@@ -125,7 +125,7 @@ public struct HTTPFields: Sendable, Hashable {
     private final class _StorageWithNIOLock: _Storage, @unchecked Sendable {
         let lock = LockStorage.create(value: ())
 
-        override func withLock<Result>(_ body: () throws -> Result) rethrows -> Result {
+        override func withLock<Result>(_ body: () throws -> sending Result) rethrows -> sending Result {
             try self.lock.withLockedValue { _ in
                 try body()
             }