diff --git a/manifests/params.pp b/manifests/params.pp
index f9bd2aaa..47a98370 100644
--- a/manifests/params.pp
+++ b/manifests/params.pp
@@ -63,7 +63,7 @@
   $cron_email_host = 'localhost'
 
   $source = ''
-  $source_dir = ''
+  $source_dir = undef
   $source_dir_purge = false
   $template = ''
   $options = ''