diff --git a/manifests/filter.pp b/manifests/filter.pp
index fa2a719..5a4834e 100644
--- a/manifests/filter.pp
+++ b/manifests/filter.pp
@@ -6,6 +6,15 @@ define fluentd::filter (
   $pattern  = '',
   $config   = {},
 ) {
+
+  # parameter validation
+  if ! ($ensure in [ 'present', 'absent' ]) {
+    fail('ensure parameter must be present or absent')
+  }
+  validate_integer($priority)
+  validate_string($pattern)
+  validate_hash($config)
+
   fluentd::config::file { "filter-${title}":
     ensure   => $ensure,
     priority => $priority,