diff --git a/docs/known-issues.md b/docs/known-issues.md
index 282bfd5c..3f617865 100644
--- a/docs/known-issues.md
+++ b/docs/known-issues.md
@@ -38,3 +38,7 @@ The following extensions are known not to be compatible with FrankenPHP:
 | Name                                                        | Reason          | Alternatives                                                                                                         |
 | ----------------------------------------------------------- | --------------- | -------------------------------------------------------------------------------------------------------------------- |
 | [imap](https://www.php.net/manual/en/imap.installation.php) | Not thread-safe | [javanile/php-imap2](https://github.com/javanile/php-imap2), [webklex/php-imap](https://github.com/Webklex/php-imap) |
+
+## get_browser
+
+The [get_browser](https://www.php.net/manual/en/function.get-browser.php) function seems to have a bad performance after a while. A workaround is to cache (e.g. with APCU) the results per User Agent, as they are static anyway.