diff --git a/setup/web_server_configuration.rst b/setup/web_server_configuration.rst
index e4fef9b3d99..603a0ba3bbd 100644
--- a/setup/web_server_configuration.rst
+++ b/setup/web_server_configuration.rst
@@ -333,6 +333,9 @@ The **minimum configuration** to get your application running under Nginx is:
             # Otherwise, PHP's OPcache may not properly detect changes to
             # your PHP files (see https://github.com/zendtech/ZendOptimizerPlus/issues/126
             # for more information).
+            # Caveat: When PHP-FPM is hosted on a different machine from nginx
+            #         $realpath_root may not resolve as you expect! In this case try using
+            #         $document_root instead.
             fastcgi_param SCRIPT_FILENAME $realpath_root$fastcgi_script_name;
             fastcgi_param DOCUMENT_ROOT $realpath_root;
             # Prevents URIs that include the front controller. This will 404: