diff --git a/REFERENCE.md b/REFERENCE.md
index faf7c2424..6a8a8fef7 100644
--- a/REFERENCE.md
+++ b/REFERENCE.md
@@ -1697,7 +1697,7 @@ The following parameters are available in the `firewall` type.
 
 namevar
 
-Data type: `Pattern[/(^\d+(?:[ \t-]\S+)+$)/]`
+Data type: `Pattern[/(^\d+(?:[ \t-_]\S+)+$)/]`
 _*this data type contains a regex that may not be accurately reflected in generated documentation_
 
       The canonical name of the rule. This name is also used for ordering
diff --git a/lib/puppet/type/firewall.rb b/lib/puppet/type/firewall.rb
index 9b4591203..65a6ea16f 100644
--- a/lib/puppet/type/firewall.rb
+++ b/lib/puppet/type/firewall.rb
@@ -133,7 +133,7 @@
       DESC
     },
     name: {
-      type: 'Pattern[/(^\d+(?:[ \t-]\S+)+$)/]',
+      type: 'Pattern[/(^\d+(?:[ \t-_]\S+)+$)/]',
       behaviour: :namevar,
       desc: <<-DESC
       The canonical name of the rule. This name is also used for ordering