diff --git a/lib/puppet/parser/functions/is_domain_name.rb b/lib/puppet/parser/functions/is_domain_name.rb
index 24cc2085f..2860dede5 100644
--- a/lib/puppet/parser/functions/is_domain_name.rb
+++ b/lib/puppet/parser/functions/is_domain_name.rb
@@ -13,6 +13,9 @@ module Puppet::Parser::Functions
         "given #{arguments.size} for 1")
     end
 
+    # Only allow string types
+    return false unless arguments[0].is_a?(String)
+
     domain = arguments[0].dup
 
     # Limits (rfc1035, 3.1)
@@ -20,9 +23,6 @@ module Puppet::Parser::Functions
     label_min_length=1
     label_max_length=63
 
-    # Only allow string types
-    return false unless domain.is_a?(String)
-
     # Allow ".", it is the top level domain
     return true if domain == '.'