diff --git a/sdktest/test/safe_patching/body.tmpl.html b/sdktest/test/safe_patching/body.tmpl.html
new file mode 100644
index 0000000..74c4d6e
--- /dev/null
+++ b/sdktest/test/safe_patching/body.tmpl.html
@@ -0,0 +1,5 @@
+<script defer>
+    ResizeObserver_toString = ResizeObserver.toString();
+</script>
+<script defer src="{{ .SiteJSPath }}"></script>
+<script defer src="main.tmpl.ts"></script>
diff --git a/sdktest/test/safe_patching/main.tmpl.ts b/sdktest/test/safe_patching/main.tmpl.ts
new file mode 100644
index 0000000..056abed
--- /dev/null
+++ b/sdktest/test/safe_patching/main.tmpl.ts
@@ -0,0 +1,14 @@
+/*!
+ * Copyright (c) Friendly Captcha GmbH 2023.
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+import { sdktest } from "../../sdktestlib/sdk.js";
+
+// This gets set in a <script> tag inlined in the HTML file.
+declare var ResizeObserver_toString: string;
+
+sdktest.test({ name: "loading the SDK doesn't break the `toString()` method for native browser objects" }, t => {
+  t.assert.equal(ResizeObserver_toString, ResizeObserver.toString());
+});