diff --git a/manifests/params/validate.pp b/manifests/params/validate.pp
index 9578b8e..fa2cbd4 100644
--- a/manifests/params/validate.pp
+++ b/manifests/params/validate.pp
@@ -47,7 +47,7 @@
   $manage_db             = '',
   $manage_db_tables      = '',
   $manage_logwatch       = '',
-  $plugin_dir            = '',
+  $plugin_dir            = undef,
   $storage_default_mount = '',
   $storage_server        = '',
   $tls_allowed_cn        = '',