diff --git a/activesupport/lib/active_support/core_ext/module/model_naming.rb b/activesupport/lib/active_support/core_ext/module/model_naming.rb
index abb02f1f70..5518f5417b 100644
--- a/activesupport/lib/active_support/core_ext/module/model_naming.rb
+++ b/activesupport/lib/active_support/core_ext/module/model_naming.rb
@@ -6,7 +6,7 @@ module ActiveSupport
       super
       @singular = underscore.tr('/', '_').freeze
       @plural = @singular.pluralize.freeze
-      @cache_key = tableize
+      @cache_key = tableize.freeze
       @partial_path = "#{@cache_key}/#{demodulize.underscore}".freeze
     end
   end