diff --git a/lib/puppet/functions/sudo/defaults.rb b/lib/puppet/functions/sudo/defaults.rb
index 1fd66d1..c5bc8cf 100644
--- a/lib/puppet/functions/sudo/defaults.rb
+++ b/lib/puppet/functions/sudo/defaults.rb
@@ -43,7 +43,7 @@ def defaults(*args)
   def defaults_entry(key, config)
     entry = "Defaults\t#{key}"
 
-    unless config.nil?
+    unless config.nil? || config.equal?(:undef)
       entry.concat((config['list']).to_s) if config.key? 'list'
 
       operator = '='