diff --git a/src/transports/windowPostMessageTransport.test.ts b/src/transports/windowPostMessageTransport.test.ts
index b0650d4..3697fca 100644
--- a/src/transports/windowPostMessageTransport.test.ts
+++ b/src/transports/windowPostMessageTransport.test.ts
@@ -230,6 +230,24 @@ describe('WindowPostMessageTransport', () => {
     expect(notificationCallback).not.toHaveBeenCalled();
   });
 
+  it('should ignore messages with non-object data', async () => {
+    await transport.connect();
+
+    expect(() =>
+      messageHandler({
+        data: null,
+        origin: mockLocation.origin,
+      } as MessageEvent),
+    ).not.toThrow();
+
+    expect(() =>
+      messageHandler({
+        data: 'unrelated message',
+        origin: mockLocation.origin,
+      } as MessageEvent),
+    ).not.toThrow();
+  });
+
   it('should handle disconnection', async () => {
     await transport.connect();
     expect(transport.isConnected()).toBe(true);
diff --git a/src/transports/windowPostMessageTransport.ts b/src/transports/windowPostMessageTransport.ts
index 5ba2ced..83c2aa6 100644
--- a/src/transports/windowPostMessageTransport.ts
+++ b/src/transports/windowPostMessageTransport.ts
@@ -93,6 +93,10 @@ export function getWindowPostMessageTransport(
 
       // Set up message listener
       messageListener = (event: MessageEvent) => {
+        if (!event.data || typeof event.data !== 'object') {
+          return;
+        }
+
         const { target, data } = event.data;
         if (target !== INPAGE || data?.name !== MULTICHAIN_SUBSTREAM_NAME || event.origin !== location.origin) {
           return;