diff --git a/Package.swift b/Package.swift
index d98c626..e3a7472 100644
--- a/Package.swift
+++ b/Package.swift
@@ -10,6 +10,9 @@ var swiftSettings: [SwiftSetting] = [
 
     // https://github.com/swiftlang/swift-evolution/blob/main/proposals/0409-access-level-on-imports.md
     .enableUpcomingFeature("InternalImportsByDefault"),
+
+    // https://github.com/swiftlang/swift-evolution/blob/main/proposals/0461-async-function-isolation.md
+    .enableUpcomingFeature("NonisolatedNonsendingByDefault"),
 ]
 
 let package = Package(
diff --git a/Sources/HBLambdaTest/maths.swift b/Sources/HBLambdaTest/maths.swift
index d23b119..f535a0d 100644
--- a/Sources/HBLambdaTest/maths.swift
+++ b/Sources/HBLambdaTest/maths.swift
@@ -16,10 +16,10 @@ typealias AppRequestContext = BasicLambdaRequestContext<APIGatewayV2Request>
 
 struct DebugMiddleware: RouterMiddleware {
     typealias Context = AppRequestContext
-    func handle(
+    @concurrent func handle(
         _ request: Request,
         context: Context,
-        next: (Request, Context) async throws -> Output
+        next: @concurrent (Request, Context) async throws -> Output
     ) async throws -> Output {
         context.logger.debug("\(request.method) \(request.uri)")
         context.logger.debug("\(context.event)")