diff --git a/manifests/certbot/config.pp b/manifests/certbot/config.pp
index af635ae..0963470 100644
--- a/manifests/certbot/config.pp
+++ b/manifests/certbot/config.pp
@@ -32,7 +32,7 @@ class cd_nagios::certbot::config (
       # ensure there is no forward vhost file
 
       exec { 'remove forward vhost':
-        command   =>  "rm -Rf  $ng_forward_conf",
+        command   =>  "rm -Rf ${ng_forward_conf}",
         creates   =>  '/etc/httpd/conf.d/.cert_created',
       }