diff --git a/source/content/guides/custom-upstream/09-troubleshooting.md b/source/content/guides/custom-upstream/09-troubleshooting.md
index 82f9cf9a84..9fa83ec7f4 100644
--- a/source/content/guides/custom-upstream/09-troubleshooting.md
+++ b/source/content/guides/custom-upstream/09-troubleshooting.md
@@ -217,6 +217,10 @@ This will trigger a "Code Cache Clear" to verify that the Site Dashboard has fet
 
 It might be necessary to reset the site's upstream via [Terminus](/terminus/examples/#switch-upstreams) if updates are still not showing on the site. Please note that only the Site Owner or owning Organization Administrators can change a site's upstream.
 
+## Unsupported PHP Versions in a Custom Upstream
+
+As PHP versions are moved to "End of Sale", existing sites will continue to run, but new sites will error during the creation step if the `php_version` value in `pantheon.upstream.yml` is no longer supported. In order to create new sites from your Custom Upstream,  update your upstream's PHP version to a supported version of PHP. For details on what PHP versions Pantheon currently supports and reccomended, see [the PHP documentation](/guides/php#supported-php-versions).
+
 ## More Resources
 
 - [Clear Upstream Cache](/terminus/commands/site-upstream-clear-cache)