diff --git a/lib/literal/types/union_type.rb b/lib/literal/types/union_type.rb
index 5a377f9..3b102cb 100644
--- a/lib/literal/types/union_type.rb
+++ b/lib/literal/types/union_type.rb
@@ -29,6 +29,7 @@ def initialize(*queue)
 		end
 
 		@types.freeze
+		freeze
 	end
 
 	attr_reader :types