diff --git a/Package.swift b/Package.swift
index cbc6ccc..c86538b 100644
--- a/Package.swift
+++ b/Package.swift
@@ -1,4 +1,4 @@
-// swift-tools-version:5.4
+// swift-tools-version:5.7
 import PackageDescription
 
 let package = Package(
diff --git a/Package@swift-5.9.swift b/Package@swift-5.9.swift
new file mode 100644
index 0000000..1e85788
--- /dev/null
+++ b/Package@swift-5.9.swift
@@ -0,0 +1,33 @@
+// swift-tools-version:5.9
+import PackageDescription
+
+let package = Package(
+    name: "multipart-kit",
+    platforms: [
+        .macOS(.v10_15),
+        .iOS(.v13),
+        .tvOS(.v13),
+        .watchOS(.v6),
+    ],
+    products: [
+        .library(name: "MultipartKit", targets: ["MultipartKit"]),
+    ],
+    dependencies: [
+        .package(url: "https://github.com/apple/swift-nio.git", from: "2.61.1"),
+        .package(url: "https://github.com/apple/swift-collections.git", from: "1.0.5")
+    ],
+    targets: [
+        .target(
+            name: "MultipartKit",
+            dependencies: [
+                .product(name: "NIO", package: "swift-nio"),
+                .product(name: "NIOHTTP1", package: "swift-nio"),
+                .product(name: "Collections", package: "swift-collections")
+            ],
+            swiftSettings: [.enableExperimentalFeature("StrictConcurrency")]),
+        .testTarget(
+            name: "MultipartKitTests",
+            dependencies: ["MultipartKit"],
+            swiftSettings: [.enableExperimentalFeature("StrictConcurrency")]),
+    ]
+)
diff --git a/Sources/MultipartKit/FormDataDecoder/FormDataDecoder.swift b/Sources/MultipartKit/FormDataDecoder/FormDataDecoder.swift
index f728bb6..7e6f2c8 100644
--- a/Sources/MultipartKit/FormDataDecoder/FormDataDecoder.swift
+++ b/Sources/MultipartKit/FormDataDecoder/FormDataDecoder.swift
@@ -6,7 +6,7 @@ import NIOHTTP1
 /// See [RFC#2388](https://tools.ietf.org/html/rfc2388) for more information about `multipart/form-data` encoding.
 ///
 /// Seealso `MultipartParser` for more information about the `multipart` encoding.
-public struct FormDataDecoder {
+public struct FormDataDecoder: Sendable {
 
     /// Maximum nesting depth to allow when decoding the input.
     /// - 1 corresponds to a single value
@@ -15,7 +15,7 @@ public struct FormDataDecoder {
     let nestingDepth: Int
 
     /// Any contextual information set by the user for decoding.
-    public var userInfo: [CodingUserInfoKey: Any] = [:]
+    public var userInfo: [CodingUserInfoKey: Sendable] = [:]
 
     /// Creates a new `FormDataDecoder`.
     /// - Parameter nestingDepth: maximum allowed nesting depth of the decoded structure. Defaults to 8.
diff --git a/Sources/MultipartKit/FormDataEncoder/FormDataEncoder.swift b/Sources/MultipartKit/FormDataEncoder/FormDataEncoder.swift
index 399c889..f48066d 100644
--- a/Sources/MultipartKit/FormDataEncoder/FormDataEncoder.swift
+++ b/Sources/MultipartKit/FormDataEncoder/FormDataEncoder.swift
@@ -5,10 +5,10 @@ import NIOCore
 /// See [RFC#2388](https://tools.ietf.org/html/rfc2388) for more information about `multipart/form-data` encoding.
 ///
 /// Seealso `MultipartParser` for more information about the `multipart` encoding.
-public struct FormDataEncoder {
+public struct FormDataEncoder: Sendable {
 
     /// Any contextual information set by the user for encoding.
-    public var userInfo: [CodingUserInfoKey: Any] = [:]
+    public var userInfo: [CodingUserInfoKey: Sendable] = [:]
 
     /// Creates a new `FormDataEncoder`.
     public init() { }
diff --git a/Sources/MultipartKit/MultipartFormData.swift b/Sources/MultipartKit/MultipartFormData.swift
index 428412c..da084b2 100644
--- a/Sources/MultipartKit/MultipartFormData.swift
+++ b/Sources/MultipartKit/MultipartFormData.swift
@@ -1,6 +1,6 @@
-import Collections
+@preconcurrency import Collections
 
-enum MultipartFormData: Equatable {
+enum MultipartFormData: Equatable, Sendable {
     typealias Keyed = OrderedDictionary<String, MultipartFormData>
 
     case single(MultipartPart)
diff --git a/Sources/MultipartKit/MultipartPart.swift b/Sources/MultipartKit/MultipartPart.swift
index e252bc7..2281fc1 100644
--- a/Sources/MultipartKit/MultipartPart.swift
+++ b/Sources/MultipartKit/MultipartPart.swift
@@ -3,7 +3,7 @@ import NIOHTTP1
 import Foundation
 
 /// A single part of a `multipart`-encoded message.
-public struct MultipartPart: Equatable {
+public struct MultipartPart: Equatable, Sendable {
     /// The part's headers.
     public var headers: HTTPHeaders
 
diff --git a/Sources/MultipartKit/MultipartSerializer.swift b/Sources/MultipartKit/MultipartSerializer.swift
index 4523785..a005dc0 100644
--- a/Sources/MultipartKit/MultipartSerializer.swift
+++ b/Sources/MultipartKit/MultipartSerializer.swift
@@ -3,7 +3,7 @@ import NIOCore
 /// Serializes `MultipartForm`s to `Data`.
 ///
 /// See `MultipartParser` for more information about the multipart encoding.
-public final class MultipartSerializer {
+public final class MultipartSerializer: Sendable {
 
     /// Creates a new `MultipartSerializer`.
     public init() { }