diff --git a/lib/lit.rb b/lib/lit.rb
index e3fa7fc5..6755f50d 100644
--- a/lib/lit.rb
+++ b/lib/lit.rb
@@ -38,6 +38,7 @@ def self.init
         Lit.included_keys = keys
       end
       Lit.included_keys = [] unless Lit.included_keys.is_a?(Array)
+      Lit.included_keys = Lit.included_keys.map(&:freeze).freeze
 
       if Lit.ignored_keys.is_a?(String)
         keys = Lit.ignored_keys.split(',').map(&:strip)