diff --git a/lib/fast_jsonapi/serialization_core.rb b/lib/fast_jsonapi/serialization_core.rb
index 6dea90e..de138cd 100644
--- a/lib/fast_jsonapi/serialization_core.rb
+++ b/lib/fast_jsonapi/serialization_core.rb
@@ -185,11 +185,7 @@ module FastJsonapi
           return object.id
         end
 
-        if relationship[:relationship_type] == :has_one
-          record.public_send(relationship[:object_method_name]).try(:id)
-        else
-          record.public_send(relationship[:id_method_name])
-        end
+        record.public_send(relationship[:id_method_name])
       end
     end
   end
diff --git a/spec/lib/object_serializer_inheritance_spec.rb b/spec/lib/object_serializer_inheritance_spec.rb
index b8ba19e..06dba25 100644
--- a/spec/lib/object_serializer_inheritance_spec.rb
+++ b/spec/lib/object_serializer_inheritance_spec.rb
@@ -30,6 +30,10 @@ describe FastJsonapi::ObjectSerializer do
       p.user_id = id
       p
     end
+
+    def photo_id
+      1
+    end
   end
 
   class UserSerializer
@@ -77,6 +81,10 @@ describe FastJsonapi::ObjectSerializer do
       a.employee_id = id
       a
     end
+
+    def account_id
+      1
+    end
   end
 
   class EmployeeSerializer < UserSerializer
diff --git a/spec/shared/contexts/movie_context.rb b/spec/shared/contexts/movie_context.rb
index 64d901d..7871f8b 100644
--- a/spec/shared/contexts/movie_context.rb
+++ b/spec/shared/contexts/movie_context.rb
@@ -31,6 +31,10 @@ RSpec.shared_context 'movie class' do
         mt
       end
 
+      def advertising_campaign_id
+        1
+      end
+
       def advertising_campaign
         ac = AdvertisingCampaign.new
         ac.id = 1
@@ -284,7 +288,7 @@ RSpec.shared_context 'movie class' do
       :owner_id,
       :owner,
       :movie_type_id,
-      :advertising_campaign
+      :advertising_campaign_id
     )
 
     ActorStruct = Struct.new(:id, :name, :email, :agency_id, :award_ids)