diff --git a/lib/money-rails/active_record/monetizable.rb b/lib/money-rails/active_record/monetizable.rb
index 35aa2eaba..4b6b5febf 100644
--- a/lib/money-rails/active_record/monetizable.rb
+++ b/lib/money-rails/active_record/monetizable.rb
@@ -10,7 +10,7 @@ class ReadOnlyCurrencyException < MoneyRails::Error; end
 
       module ClassMethods
         def monetized_attributes
-          monetized_attributes = @monetized_attributes || {}
+          monetized_attributes = @monetized_attributes || {}.with_indifferent_access
 
           if superclass.respond_to?(:monetized_attributes)
             monetized_attributes.merge(superclass.monetized_attributes)