diff --git a/src/jrpc/postMessageStream.ts b/src/jrpc/postMessageStream.ts
index 66de21c5..ba675338 100644
--- a/src/jrpc/postMessageStream.ts
+++ b/src/jrpc/postMessageStream.ts
@@ -4,10 +4,13 @@ import { cloneDeep } from "../utils";
 import { BasePostMessageStream, isValidStreamMessage, type PostMessageEvent } from "./basePostMessageStream";
 
 /* istanbul ignore next */
-const getSource = Object.getOwnPropertyDescriptor(MessageEvent.prototype, "source")?.get;
+const messageEventPrototype = typeof MessageEvent === "undefined" ? undefined : MessageEvent.prototype;
 
 /* istanbul ignore next */
-const getOrigin = Object.getOwnPropertyDescriptor(MessageEvent.prototype, "origin")?.get;
+const getSource = messageEventPrototype ? Object.getOwnPropertyDescriptor(messageEventPrototype, "source")?.get : undefined;
+
+/* istanbul ignore next */
+const getOrigin = messageEventPrototype ? Object.getOwnPropertyDescriptor(messageEventPrototype, "origin")?.get : undefined;
 
 export interface PostMessageStreamArgs extends DuplexOptions {
   name: string;
diff --git a/test/postMessageStream.test.ts b/test/postMessageStream.test.ts
index 5e133d68..6af0f5b4 100644
--- a/test/postMessageStream.test.ts
+++ b/test/postMessageStream.test.ts
@@ -72,4 +72,12 @@ describe("PostMessageStream", () => {
     expect(message.target).toBe("auth");
     expect(message.data.data.params[0]._origin).toBe("https://current.example");
   });
+
+  it("can be imported when MessageEvent is undefined", async () => {
+    vi.unstubAllGlobals();
+    // Simulate Hermes/React Native where MessageEvent is absent.
+    Reflect.deleteProperty(globalThis, "MessageEvent");
+
+    await expect(import("../src/jrpc")).resolves.toHaveProperty("PostMessageStream");
+  });
 });