diff --git a/pxtservices/iframeEmbeddedClient.ts b/pxtservices/iframeEmbeddedClient.ts
index c98465fd14b..4aef1c28df6 100644
--- a/pxtservices/iframeEmbeddedClient.ts
+++ b/pxtservices/iframeEmbeddedClient.ts
@@ -63,7 +63,7 @@ export class IFrameEmbeddedClient {
         else if ((window as any).acquireVsCodeApi) {
             (window as any).acquireVsCodeApi().postMessage(message)
         }
-        else {
+        else if (window.parent && window.parent !== window) {
             window.parent.postMessage(message, "*");
         }
     }