diff --git a/CHANGELOG.md b/CHANGELOG.md
index 43c0d122..561f686e 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -3,6 +3,8 @@ Changelog
 
 ## master
 
+- Fixed: `@_spi` errors (#339)
+
 ## [0.11.0]
 
 - Added: visionOS support (#327)
diff --git a/Sources/Introspect.swift b/Sources/Introspect.swift
index 272f0e89..58fcae89 100644
--- a/Sources/Introspect.swift
+++ b/Sources/Introspect.swift
@@ -108,6 +108,17 @@ public protocol PlatformEntity: AnyObject {
     func isDescendant(of other: Base) -> Bool
 }
 
+extension PlatformEntity {
+    @_spi(Internals)
+    public var ancestor: Base? { nil }
+
+    @_spi(Internals)
+    public var descendants: [Base] { [] }
+
+    @_spi(Internals)
+    public func isDescendant(of other: Base) -> Bool { false }
+}
+
 extension PlatformEntity {
     @_spi(Internals)
     public var ancestors: some Sequence<Base> {
@@ -196,24 +207,10 @@ extension PlatformViewController: PlatformEntity {
 
 #if canImport(UIKit)
 extension UIPresentationController: PlatformEntity {
-    @_spi(Internals)
-    public var ancestor: UIPresentationController? { nil }
-
-    @_spi(Internals)
-    public var descendants: [UIPresentationController] { [] }
-
-    @_spi(Internals)
-    public func isDescendant(of other: UIPresentationController) -> Bool { false }
+    public typealias Base = UIPresentationController
 }
 #elseif canImport(AppKit)
 extension NSWindow: PlatformEntity {
-    @_spi(Internals)
-    public var ancestor: NSWindow? { nil }
-
-    @_spi(Internals)
-    public var descendants: [NSWindow] { [] }
-
-    @_spi(Internals)
-    public func isDescendant(of other: NSWindow) -> Bool { false }
+    public typealias Base = NSWindow
 }
 #endif