diff --git a/config/initializers/hexapdf.rb b/config/initializers/hexapdf.rb
index 7562ee72..a8dd5203 100644
--- a/config/initializers/hexapdf.rb
+++ b/config/initializers/hexapdf.rb
@@ -112,6 +112,8 @@ module HexaPDF
   end
 
   module CycleSafeInheritedValue
+    using HexaPDF::Type::AcroForm::Field::HashRefinement
+
     def inherited_value(field, name)
       seen = Set.new.compare_by_identity
       seen << field.value