diff --git a/lib/active_model/serializer.rb b/lib/active_model/serializer.rb
index dd82e976..e8f52e57 100644
--- a/lib/active_model/serializer.rb
+++ b/lib/active_model/serializer.rb
@@ -72,7 +72,10 @@ end
       alias root= _root=
 
       def root_name
-        name.demodulize.underscore.sub(/_serializer$/, '') if name
+        if name
+          root_name = name.demodulize.underscore.sub(/_serializer$/, '')
+          CONFIG.plural_default_root ? root_name.pluralize : root_name
+        end
       end
 
       def attributes(*attrs)
diff --git a/test/unit/active_model/serializer/config_test.rb b/test/unit/active_model/serializer/config_test.rb
index b297f998..bd9ae48a 100644
--- a/test/unit/active_model/serializer/config_test.rb
+++ b/test/unit/active_model/serializer/config_test.rb
@@ -78,6 +78,9 @@ module ActiveModel
           assert !association.embed_objects?
           assert association.embed_in_root
           assert_equal :lower_camel, association.key_format
+          assert_equal 'post', PostSerializer.root_name
+          CONFIG.plural_default_root = true
+          assert_equal 'posts', PostSerializer.root_name
         ensure
           PostSerializer._associations[:comments] = old_association
           CONFIG.clear