diff --git a/Package.swift b/Package.swift
index c1ea0aa..fd0151d 100644
--- a/Package.swift
+++ b/Package.swift
@@ -1,4 +1,4 @@
-// swift-tools-version:5.1
+// swift-tools-version: 6.2
 
 import PackageDescription
 
@@ -13,11 +13,15 @@ let package = Package(
     targets: [
         .target(
             name: "PythonKit",
-            path: "PythonKit"
+            path: "PythonKit",
+            swiftSettings: [
+                .defaultIsolation(MainActor.self)
+            ]
         ),
         .testTarget(
             name: "PythonKitTests",
             dependencies: ["PythonKit"]
         ),
-    ]
+    ],
+    swiftLanguageModes: [.v5]
 )
diff --git a/PythonKit/Python.swift b/PythonKit/Python.swift
index 35d2fcb..87cf6cf 100644
--- a/PythonKit/Python.swift
+++ b/PythonKit/Python.swift
@@ -37,7 +37,7 @@ typealias OwnedPyObjectPointer = PyObjectPointer
 //   `PythonObject` will define copy constructors, move constructors, etc. to
 //   implement move semantics.
 @usableFromInline @_fixed_layout
-final class PyReference {
+nonisolated final class PyReference {
     private var pointer: OwnedPyObjectPointer
 
     // This `PyReference`, once deleted, will make no delta change to the
@@ -207,6 +207,7 @@ public extension PythonObject {
 }
 
 /// An error produced by a failable Python operation.
+@MainActor
 public enum PythonError : Error, Equatable {
     /// A Python runtime exception, produced by calling a Python function.
     case exception(PythonObject, traceback: PythonObject?)
diff --git a/PythonKit/PythonLibrary.swift b/PythonKit/PythonLibrary.swift
index ab94a3f..55afb3d 100644
--- a/PythonKit/PythonLibrary.swift
+++ b/PythonKit/PythonLibrary.swift
@@ -30,6 +30,7 @@ import WinSDK
 //===----------------------------------------------------------------------===//
 
 public struct PythonLibrary {
+    @MainActor
     public enum Error: Swift.Error, Equatable, CustomStringConvertible {
         case pythonLibraryNotFound