diff --git a/Package@swift-5.9.swift b/Package@swift-5.9.swift
new file mode 100644
index 0000000..8866f19
--- /dev/null
+++ b/Package@swift-5.9.swift
@@ -0,0 +1,39 @@
+// swift-tools-version:5.9
+
+import PackageDescription
+
+let package = Package(
+  name: "swift-custom-dump",
+  platforms: [
+    .iOS(.v13),
+    .macOS(.v10_15),
+    .tvOS(.v13),
+    .watchOS(.v6),
+  ],
+  products: [
+    .library(
+      name: "CustomDump",
+      targets: ["CustomDump"]
+    )
+  ],
+  dependencies: [
+    .package(url: "https://github.com/pointfreeco/xctest-dynamic-overlay", from: "1.0.0")
+  ],
+  targets: [
+    .target(
+      name: "CustomDump",
+      dependencies: [
+        .product(name: "XCTestDynamicOverlay", package: "xctest-dynamic-overlay")
+      ],
+      swiftSettings: [
+        .enableExperimentalFeature("StrictConcurrency")
+      ]
+    ),
+    .testTarget(
+      name: "CustomDumpTests",
+      dependencies: [
+        "CustomDump"
+      ]
+    ),
+  ]
+)
diff --git a/Sources/CustomDump/Diff.swift b/Sources/CustomDump/Diff.swift
index 1f61b38..f357b77 100644
--- a/Sources/CustomDump/Diff.swift
+++ b/Sources/CustomDump/Diff.swift
@@ -753,7 +753,7 @@ public func diff<T>(_ lhs: T, _ rhs: T, format: DiffFormat = .default) -> String
 ///
 /// This type comes with two pre-configured formats that you will probably want to use for most
 /// situations: ``DiffFormat/default`` and ``DiffFormat/proportional``.
-public struct DiffFormat {
+public struct DiffFormat: Sendable {
   /// A string prepended to lines that only appear in the string representation of the first value,
   /// e.g. a "removal."
   public var first: String