diff --git a/docs/sdks/flutter/GETTING_STARTED.md b/docs/sdks/flutter/GETTING_STARTED.md
index 8d239402b3..c3a1a8d33d 100644
--- a/docs/sdks/flutter/GETTING_STARTED.md
+++ b/docs/sdks/flutter/GETTING_STARTED.md
@@ -56,13 +56,25 @@ For web in order to capture the OAuth2 callback URL and send it to the applicati
 ```html
 <!DOCTYPE html>
 <title>Authentication complete</title>
-<p>Authentication is complete. If this does not happen automatically, please
-close the window.
+<p>Authentication is complete. If this does not happen automatically, please close the window.</p>
 <script>
-  window.opener.postMessage({
-    'flutter-web-auth-2': window.location.href
-  }, window.location.origin);
-  window.close();
+  function postAuthenticationMessage() {
+    const message = {
+      'flutter-web-auth-2': window.location.href
+    };
+
+    if (window.opener) {
+      window.opener.postMessage(message, window.location.origin);
+      window.close();
+    } else if (window.parent && window.parent !== window) {
+      window.parent.postMessage(message, window.location.origin);
+    } else {
+      localStorage.setItem('flutter-web-auth-2', window.location.href);
+      window.close();
+    }
+  }
+
+  postAuthenticationMessage();
 </script>
 ```
 
