diff --git a/docs/content/4.sdk/6.migration-guide.md b/docs/content/4.sdk/6.migration-guide.md
index ac58f34ce5..7e7fd97ece 100644
--- a/docs/content/4.sdk/6.migration-guide.md
+++ b/docs/content/4.sdk/6.migration-guide.md
@@ -117,6 +117,10 @@ export default MyDocument;
 
 ```
 
+:::warning
+`__ENV.js` script is used to pass runtime environment variables to the browser. It will block rendering of the page until the script is loaded, which will slow down the page load. We recommend upgrading to the App Router and using the newest version of `next-runtime-env` to avoid this issue.
+:::
+
 5. Update SSR cache control
 
 ```ts