diff --git a/lib/active_model/serializer/adapter/json_api.rb b/lib/active_model/serializer/adapter/json_api.rb
index c1e5c94f1..e50f17cc6 100644
--- a/lib/active_model/serializer/adapter/json_api.rb
+++ b/lib/active_model/serializer/adapter/json_api.rb
@@ -43,7 +43,7 @@ def serializable_hash(options = nil)
 
         def fragment_cache(cached_hash, non_cached_hash)
           root = false if @options.include?(:include)
-          ActiveModel::Serializer::Adapter::JsonApi::FragmentCache.new().fragment_cache(root, cached_hash, non_cached_hash)
+          ActiveModel::Serializer::Adapter::JsonApi::FragmentCache.new.fragment_cache(root, cached_hash, non_cached_hash)
         end
 
         private
@@ -56,12 +56,6 @@ def resource_identifier_type_for(serializer)
           end
         end
 
-        def add_relationships(resource, name, serializers)
-          resource[:relationships] ||= {}
-          resource[:relationships][name] ||= { data: [] }
-          resource[:relationships][name][:data] += serializers.map { |serializer| { type: serializer.json_api_type, id: serializer.id.to_s } }
-        end
-
         def resource_identifier_id_for(serializer)
           if serializer.respond_to?(:id)
             serializer.id