diff --git a/lib/active_model/serializer/lazy_association.rb b/lib/active_model/serializer/lazy_association.rb
index ed7bd65c2..4ae164036 100644
--- a/lib/active_model/serializer/lazy_association.rb
+++ b/lib/active_model/serializer/lazy_association.rb
@@ -53,7 +53,7 @@ def serializer_class
       private
 
       def cached_result
-        @cached_result ||= {}
+        @cached_result ||= Concurrent::Map.new
       end
 
       def serialize_object!(object)