diff --git a/macos/GhosttyUITests/GhosttyCustomConfigCase.swift b/macos/GhosttyUITests/GhosttyCustomConfigCase.swift
index 41993247a..ca3f56677 100644
--- a/macos/GhosttyUITests/GhosttyCustomConfigCase.swift
+++ b/macos/GhosttyUITests/GhosttyCustomConfigCase.swift
@@ -27,6 +27,8 @@ class GhosttyCustomConfigCase: XCTestCase {
         true
     }
 
+    static let defaultsSuiteName: String = "GHOSTTY_UI_TESTS"
+
     var configFile: URL?
     override func setUpWithError() throws {
         continueAfterFailure = false
@@ -47,13 +49,14 @@ class GhosttyCustomConfigCase: XCTestCase {
         try newConfig.write(to: configFile!, atomically: true, encoding: .utf8)
     }
 
-    func ghosttyApplication() throws -> XCUIApplication {
+    func ghosttyApplication(defaultsSuite: String = GhosttyCustomConfigCase.defaultsSuiteName) throws -> XCUIApplication {
         let app = XCUIApplication()
         app.launchArguments.append(contentsOf: ["-ApplePersistenceIgnoreState", "YES"])
         guard let configFile else {
             return app
         }
         app.launchEnvironment["GHOSTTY_CONFIG_PATH"] = configFile.path
+        app.launchEnvironment["GHOSTTY_USER_DEFAULTS_SUITE"] = defaultsSuite
         return app
     }
 }
diff --git a/macos/Sources/App/macOS/AppDelegate.swift b/macos/Sources/App/macOS/AppDelegate.swift
index c8538c9d5..b02337e4b 100644
--- a/macos/Sources/App/macOS/AppDelegate.swift
+++ b/macos/Sources/App/macOS/AppDelegate.swift
@@ -175,7 +175,15 @@ class AppDelegate: NSObject,
     // MARK: - NSApplicationDelegate
 
     func applicationWillFinishLaunching(_ notification: Notification) {
-        UserDefaults.standard.register(defaults: [
+        #if DEBUG
+        if
+            let suite = UserDefaults.ghosttySuite,
+            let clear = ProcessInfo.processInfo.environment["GHOSTTY_CLEAR_USER_DEFAULTS"],
+            (clear as NSString).boolValue {
+            UserDefaults.ghostty.removePersistentDomain(forName: suite)
+        }
+        #endif
+        UserDefaults.ghostty.register(defaults: [
             // Disable the automatic full screen menu item because we handle
             // it manually.
             "NSFullScreenMenuItemEverywhere": false,
@@ -194,7 +202,7 @@ class AppDelegate: NSObject,
 
     func applicationDidFinishLaunching(_ notification: Notification) {
         // System settings overrides
-        UserDefaults.standard.register(defaults: [
+        UserDefaults.ghostty.register(defaults: [
             // Disable this so that repeated key events make it through to our terminal views.
             "ApplePressAndHoldEnabled": false,
         ])
@@ -203,7 +211,7 @@ class AppDelegate: NSObject,
         applicationLaunchTime = ProcessInfo.processInfo.systemUptime
 
         // Check if secure input was enabled when we last quit.
-        if UserDefaults.standard.bool(forKey: "SecureInput") != SecureInput.shared.enabled {
+        if UserDefaults.ghostty.bool(forKey: "SecureInput") != SecureInput.shared.enabled {
             toggleSecureInput(self)
         }
 
@@ -747,10 +755,10 @@ class AppDelegate: NSObject,
         // configuration. This is the only way to carefully control whether macOS invokes the
         // state restoration system.
         switch config.windowSaveState {
-        case "never": UserDefaults.standard.setValue(false, forKey: "NSQuitAlwaysKeepsWindows")
-        case "always": UserDefaults.standard.setValue(true, forKey: "NSQuitAlwaysKeepsWindows")
+        case "never": UserDefaults.ghostty.setValue(false, forKey: "NSQuitAlwaysKeepsWindows")
+        case "always": UserDefaults.ghostty.setValue(true, forKey: "NSQuitAlwaysKeepsWindows")
         case "default": fallthrough
-        default: UserDefaults.standard.removeObject(forKey: "NSQuitAlwaysKeepsWindows")
+        default: UserDefaults.ghostty.removeObject(forKey: "NSQuitAlwaysKeepsWindows")
         }
 
         // Sync our auto-update settings. If SUEnableAutomaticChecks (in our Info.plist) is
@@ -835,9 +843,9 @@ class AppDelegate: NSObject,
     private func updateAppIcon(from config: Ghostty.Config) {
         // Since this is called after `DockTilePlugin` has been running,
         // clean it up here to trigger a correct update of the current config.
-        UserDefaults.standard.removeObject(forKey: "CustomGhosttyIcon")
+        UserDefaults.ghostty.removeObject(forKey: "CustomGhosttyIcon")
         DispatchQueue.global().async {
-            UserDefaults.standard.appIcon = AppIcon(config: config)
+            UserDefaults.ghostty.appIcon = AppIcon(config: config)
             DistributedNotificationCenter.default()
                 .postNotificationName(.ghosttyIconDidChange, object: nil, userInfo: nil, deliverImmediately: true)
         }
@@ -927,7 +935,7 @@ class AppDelegate: NSObject,
             input.global.toggle()
         }
         self.menuSecureInput?.state = if input.global { .on } else { .off }
-        UserDefaults.standard.set(input.global, forKey: "SecureInput")
+        UserDefaults.ghostty.set(input.global, forKey: "SecureInput")
     }
 
     // MARK: - IB Actions
@@ -1321,7 +1329,7 @@ extension AppDelegate {
     }
 
     @IBAction func useAsDefault(_ sender: NSMenuItem) {
-        let ud = UserDefaults.standard
+        let ud = UserDefaults.ghostty
         let key = TerminalWindow.defaultLevelKey
         if menuFloatOnTop?.state == .on {
             ud.set(NSWindow.Level.floating, forKey: key)
diff --git a/macos/Sources/Features/Terminal/Window Styles/TerminalWindow.swift b/macos/Sources/Features/Terminal/Window Styles/TerminalWindow.swift
index 560f45207..b9ca1ecc4 100644
--- a/macos/Sources/Features/Terminal/Window Styles/TerminalWindow.swift	
+++ b/macos/Sources/Features/Terminal/Window Styles/TerminalWindow.swift	
@@ -171,7 +171,7 @@ class TerminalWindow: NSWindow {
         tab.accessoryView = stackView
 
         // Get our saved level
-        level = UserDefaults.standard.value(forKey: Self.defaultLevelKey) as? NSWindow.Level ?? .normal
+        level = UserDefaults.ghostty.value(forKey: Self.defaultLevelKey) as? NSWindow.Level ?? .normal
     }
 
     // Both of these must be true for windows without decorations to be able to
diff --git a/macos/Sources/Ghostty/Surface View/SurfaceView_AppKit.swift b/macos/Sources/Ghostty/Surface View/SurfaceView_AppKit.swift
index c4f03b117..3129acfba 100644
--- a/macos/Sources/Ghostty/Surface View/SurfaceView_AppKit.swift	
+++ b/macos/Sources/Ghostty/Surface View/SurfaceView_AppKit.swift	
@@ -1070,7 +1070,7 @@ extension Ghostty {
 
             // If the user has force click enabled then we do a quick look. There
             // is no public API for this as far as I can tell.
-            guard UserDefaults.standard.bool(forKey: "com.apple.trackpad.forceClick") else { return }
+            guard UserDefaults.ghostty.bool(forKey: "com.apple.trackpad.forceClick") else { return }
             quickLook(with: event)
         }
 
diff --git a/macos/Sources/Helpers/Extensions/NSScreen+Extension.swift b/macos/Sources/Helpers/Extensions/NSScreen+Extension.swift
index ca338f102..84553ed34 100644
--- a/macos/Sources/Helpers/Extensions/NSScreen+Extension.swift
+++ b/macos/Sources/Helpers/Extensions/NSScreen+Extension.swift
@@ -18,7 +18,7 @@ extension NSScreen {
     // AND present on this screen.
     var hasDock: Bool {
         // If the dock autohides then we don't have a dock ever.
-        if let dockAutohide = UserDefaults.standard.persistentDomain(forName: "com.apple.dock")?["autohide"] as? Bool {
+        if let dockAutohide = UserDefaults.ghostty.persistentDomain(forName: "com.apple.dock")?["autohide"] as? Bool {
             if dockAutohide { return false }
         }
 
diff --git a/macos/Sources/Helpers/Extensions/UserDefaults+Extension.swift b/macos/Sources/Helpers/Extensions/UserDefaults+Extension.swift
new file mode 100644
index 000000000..7cd0e12ed
--- /dev/null
+++ b/macos/Sources/Helpers/Extensions/UserDefaults+Extension.swift
@@ -0,0 +1,15 @@
+import Foundation
+
+extension UserDefaults {
+    static var ghosttySuite: String? {
+        #if DEBUG
+        ProcessInfo.processInfo.environment["GHOSTTY_USER_DEFAULTS_SUITE"]
+        #else
+        nil
+        #endif
+    }
+
+    static var ghostty: UserDefaults {
+        ghosttySuite.flatMap(UserDefaults.init(suiteName:)) ?? .standard
+    }
+}
diff --git a/macos/Sources/Helpers/LastWindowPosition.swift b/macos/Sources/Helpers/LastWindowPosition.swift
index 933eba394..298367c74 100644
--- a/macos/Sources/Helpers/LastWindowPosition.swift
+++ b/macos/Sources/Helpers/LastWindowPosition.swift
@@ -15,7 +15,7 @@ class LastWindowPosition {
         guard let window, window.isVisible else { return false }
         let frame = window.frame
         let rect = [frame.origin.x, frame.origin.y, frame.size.width, frame.size.height]
-        UserDefaults.standard.set(rect, forKey: positionKey)
+        UserDefaults.ghostty.set(rect, forKey: positionKey)
         return true
     }
 
@@ -32,7 +32,7 @@ class LastWindowPosition {
     func restore(_ window: NSWindow, origin restoreOrigin: Bool = true, size restoreSize: Bool = true) -> Bool {
         guard restoreOrigin || restoreSize else { return false }
 
-        guard let values = UserDefaults.standard.array(forKey: positionKey) as? [Double],
+        guard let values = UserDefaults.ghostty.array(forKey: positionKey) as? [Double],
               values.count >= 2 else { return false }
 
         let lastPosition = CGPoint(x: values[0], y: values[1])
diff --git a/macos/Sources/Helpers/PermissionRequest.swift b/macos/Sources/Helpers/PermissionRequest.swift
index 29d1ab6d3..0308a0204 100644
--- a/macos/Sources/Helpers/PermissionRequest.swift
+++ b/macos/Sources/Helpers/PermissionRequest.swift
@@ -126,7 +126,7 @@ class PermissionRequest {
     /// - Parameter key: The UserDefaults key to check
     /// - Returns: The cached decision, or nil if no valid cached decision exists
     private static func getStoredResult(for key: String) -> Bool? {
-        let userDefaults = UserDefaults.standard
+        let userDefaults = UserDefaults.ghostty
         guard let data = userDefaults.data(forKey: key),
               let storedPermission = try? NSKeyedUnarchiver.unarchivedObject(
                 ofClass: StoredPermission.self, from: data) else {
@@ -151,7 +151,7 @@ class PermissionRequest {
         let expiryDate = Date().addingTimeInterval(duration.timeInterval)
         let storedPermission = StoredPermission(result: result, expiry: expiryDate)
         if let data = try? NSKeyedArchiver.archivedData(withRootObject: storedPermission, requiringSecureCoding: true) {
-            let userDefaults = UserDefaults.standard
+            let userDefaults = UserDefaults.ghostty
             userDefaults.set(data, forKey: key)
         }
     }