diff --git a/packages/runtime/src/index.ts b/packages/runtime/src/index.ts
index dc03137..6fd2a8c 100644
--- a/packages/runtime/src/index.ts
+++ b/packages/runtime/src/index.ts
@@ -1,3 +1,5 @@
+// Polyfills must be imported first to ensure compatibility with Hermes
+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..4410462
--- /dev/null
+++ b/packages/runtime/src/polyfills.ts
@@ -0,0 +1,16 @@
+/**
+ * Polyfills for Hermes JavaScript engine compatibility.
+ *
+ * Hermes (React Native's default JS engine) doesn't support all ES2022+ features.
+ * This file provides polyfills for features used by harness dependencies.
+ */
+
+/**
+ * Object.hasOwn (ES2022)
+ * Used by @vitest/expect v4.x for property checking.
+ * @see https://github.com/facebook/hermes/issues/1875
+ */
+if (typeof Object.hasOwn !== 'function') {
+  Object.hasOwn = (obj: object, prop: PropertyKey): boolean =>
+    Object.prototype.hasOwnProperty.call(obj, prop);
+}