diff --git a/main.js b/main.js
index 36ccf4b..c8d1410 100644
--- a/main.js
+++ b/main.js
@@ -1543,13 +1543,13 @@ class ApplicationController {
     } else if (this.isReady) {
       // When app is activated, ensure windows appear on current desktop
       const mainWindow = windowManager.getWindow("main");
-      if (mainWindow && mainWindow.isVisible()) {
+      if (mainWindow && !mainWindow.isDestroyed() && mainWindow.isVisible()) {
         windowManager.showOnCurrentDesktop(mainWindow);
       }
 
       // Also handle other visible windows
       windowManager.windows.forEach((window, type) => {
-        if (window.isVisible()) {
+        if (!window.isDestroyed() && window.isVisible()) {
           windowManager.showOnCurrentDesktop(window);
         }
       });
diff --git a/src/managers/window.manager.js b/src/managers/window.manager.js
index 52fa81b..22afac1 100644
--- a/src/managers/window.manager.js
+++ b/src/managers/window.manager.js
@@ -1365,6 +1365,16 @@ class WindowManager {
       onboardingWindow = await this.createWindow('onboarding');
       this.windows.set('onboarding', onboardingWindow);
 
+      // The 'closed' handlers in setupWindowEventHandlers() are wired once,
+      // at startup, over the windows that exist then. The onboarding wizard
+      // is created later, so it needs its own handler — otherwise its entry
+      // outlives the BrowserWindow and later iterations over this.windows
+      // call methods on a destroyed object.
+      onboardingWindow.on('closed', () => {
+        logger.debug('Window closed', { type: 'onboarding' });
+        this.windows.delete('onboarding');
+      });
+
       // Once the wizard renderer signals it's ready, send it the
       // current first-run status so it can pre-populate correctly.
       onboardingWindow.webContents.once('did-finish-load', () => {