diff --git a/website/docs/r/app.html.markdown b/website/docs/r/app.html.markdown
index bc10994a..50f2637b 100644
--- a/website/docs/r/app.html.markdown
+++ b/website/docs/r/app.html.markdown
@@ -42,6 +42,9 @@ The following arguments are supported:
      Buildpacks configured externally won't be altered if this is not present.
 * `config_vars` - (Optional) Configuration variables for the application.
      The config variables in this map are not the final set of configuration
+     variables, but rather variables you want present. That is, other
+     configuration variables set externally won't be removed by Terraform
+     if they aren't present in this list.
 * `space` - (Optional) The name of a private space to create the app in.
 * `organization` - (Optional) A block that can be specified once to define
      organization settings for this app. The fields for this block are