diff --git a/lib/active_model/serializer/adapter/json_api.rb b/lib/active_model/serializer/adapter/json_api.rb
index 175d6770..a7ca89a7 100644
--- a/lib/active_model/serializer/adapter/json_api.rb
+++ b/lib/active_model/serializer/adapter/json_api.rb
@@ -126,7 +126,7 @@ module ActiveModel
 
         def serialized_object_type(serializer)
           return false unless Array(serializer).first
-          type_name = Array(serializer).first.object.class.to_s.underscore
+          type_name = Array(serializer).first.object.class.to_s.demodulize.underscore
           if serializer.respond_to?(:first)
             type_name.pluralize
           else