diff --git a/.changes/appwindow-type-fix.md b/.changes/appwindow-type-fix.md
new file mode 100644
index 00000000000..a0a6547448d
--- /dev/null
+++ b/.changes/appwindow-type-fix.md
@@ -0,0 +1,5 @@
+---
+"api": patch
+---
+
+Properly define the `appWindow` type.
diff --git a/tooling/api/rollup.config.js b/tooling/api/rollup.config.js
index d4f117bec4a..6f10739d6e6 100644
--- a/tooling/api/rollup.config.js
+++ b/tooling/api/rollup.config.js
@@ -53,7 +53,8 @@ export default [
       }),
       babel({
         configFile: false,
-        presets: [['@babel/preset-env'], ['@babel/preset-typescript']]
+        presets: [['@babel/preset-env'], ['@babel/preset-typescript']],
+        babelHelpers: 'bundled'
       }),
       terser()
     ],
diff --git a/tooling/api/src/window.ts b/tooling/api/src/window.ts
index 5d26d55a3dd..8fb96dcaac5 100644
--- a/tooling/api/src/window.ts
+++ b/tooling/api/src/window.ts
@@ -1168,7 +1168,7 @@ class WebviewWindow extends WindowManager {
 }
 
 /** The WebviewWindow for the current window. */
-let appWindow
+let appWindow: WebviewWindow
 if ('__TAURI_METADATA__' in window) {
   appWindow = new WebviewWindow(
     window.__TAURI_METADATA__.__currentWindow.label,