diff --git a/README.md b/README.md
index b954b023f1f871..d1c7e28bb5bb8e 100644
--- a/README.md
+++ b/README.md
@@ -23,8 +23,9 @@ Feel free to stop by our [Matrix room](https://chat.mozilla.org/#/room/#pdfjs:mo
 
 ### Online demo
 
-Please note that the "Modern browsers" version assumes native support for
-features such as e.g. `async`/`await`, and `ReadableStream`.
+Please note that the "Modern browsers" version assumes native support for modern
+features such as e.g. `async`/`await`, `ReadableStream`, optional chaining, and
+nullish coalescing.
 
 + Modern browsers: https://mozilla.github.io/pdf.js/web/viewer.html
 
diff --git a/external/dist/README.md b/external/dist/README.md
index 6baa2e5809961d..75109c2bbb6d98 100644
--- a/external/dist/README.md
+++ b/external/dist/README.md
@@ -7,7 +7,8 @@ parsing and rendering PDFs.
 This is a pre-built version of the PDF.js source code. It is automatically
 generated by the build scripts.
 
-For usage with older browsers/environments, without support for modern features
-such as e.g. `async`/`await`, and `ReadableStream`, please see the `es5` folder.
+For usage with older browsers or environments, without support for modern
+features such as e.g. `async`/`await`, `ReadableStream`, optional chaining, and
+nullish coalescing; please see the `es5` folder.
 
 See https://github.com/mozilla/pdf.js for learning and contributing.