diff --git a/.nx/version-plans/version-plan-1768220533507.md b/.nx/version-plans/version-plan-1768220533507.md
new file mode 100644
index 0000000..4462d45
--- /dev/null
+++ b/.nx/version-plans/version-plan-1768220533507.md
@@ -0,0 +1,5 @@
+---
+__default__: prerelease
+---
+
+Adds Object.hasOwn polyfill to the runtime package for JSC (JavaScriptCore) compatibility.
diff --git a/packages/runtime/src/index.ts b/packages/runtime/src/index.ts
index dc03137..1dc1c6e 100644
--- a/packages/runtime/src/index.ts
+++ b/packages/runtime/src/index.ts
@@ -1,3 +1,4 @@
+import './polyfills.js';
 import './globals.d.ts';
 
 export { UI as ReactNativeHarness } from './ui/index.js';
diff --git a/packages/runtime/src/polyfills.ts b/packages/runtime/src/polyfills.ts
new file mode 100644
index 0000000..df8ed18
--- /dev/null
+++ b/packages/runtime/src/polyfills.ts
@@ -0,0 +1,14 @@
+/**
+ * Polyfills for ES2022+ features not supported by JSC (JavaScriptCore).
+ *
+ * JSC, used in React Native when Hermes is disabled, doesn't support
+ * Object.hasOwn (ES2022). This causes runtime errors when @vitest/expect
+ * v4.x initializes.
+ *
+ * This polyfill must be loaded before any code that uses Object.hasOwn.
+ */
+
+if (typeof Object.hasOwn !== 'function') {
+  Object.hasOwn = (obj: object, prop: PropertyKey): boolean =>
+    Object.prototype.hasOwnProperty.call(obj, prop);
+}