diff --git a/Package.swift b/Package.swift
index 61c6c98..28a3792 100644
--- a/Package.swift
+++ b/Package.swift
@@ -1,4 +1,4 @@
-// swift-tools-version: 5.10
+// swift-tools-version: 5.9
 
 import PackageDescription
 
diff --git a/Sources/Subprocess/SubprocessDependencyBuilder.swift b/Sources/Subprocess/SubprocessDependencyBuilder.swift
index f924753..75cfe16 100644
--- a/Sources/Subprocess/SubprocessDependencyBuilder.swift
+++ b/Sources/Subprocess/SubprocessDependencyBuilder.swift
@@ -56,7 +56,12 @@ public protocol SubprocessDependencyFactory {
 /// Default implementation of SubprocessDependencyFactory
 public struct SubprocessDependencyBuilder: SubprocessDependencyFactory {
     private static let queue = DispatchQueue(label: "\(Self.self)")
+
+    #if compiler(<5.10)
+    private static var _shared: any SubprocessDependencyFactory = SubprocessDependencyBuilder()
+    #else
     nonisolated(unsafe) private static var _shared: any SubprocessDependencyFactory = SubprocessDependencyBuilder()
+    #endif
     /// Shared instance used for dependency creation
     public static var shared: any SubprocessDependencyFactory {
         get {