diff --git a/docs/static/configuration.asciidoc b/docs/static/configuration.asciidoc
index 72aaeae57..25ede16e4 100644
--- a/docs/static/configuration.asciidoc
+++ b/docs/static/configuration.asciidoc
@@ -601,6 +601,9 @@ output {
 
 [[environment-variables]]
 === Using Environment Variables in Configuration
+
+This feature is _experimental_, to enable it you will need to run logstash with the `--allow-env` flag.
+
 ==== Overview
 
 * You can set environment variable references into Logstash plugins configuration using `${var}` or `$var`.