diff --git a/lib/oat/adapters/json_api.rb b/lib/oat/adapters/json_api.rb
index 9c72515..1ef5857 100644
--- a/lib/oat/adapters/json_api.rb
+++ b/lib/oat/adapters/json_api.rb
@@ -150,6 +150,8 @@ def entity_without_root(obj, serializer_class = nil, &block)
       PLURAL = /s$/
 
       def pluralize(str)
+        return str.pluralize if str.respond_to?(:pluralize)
+        
         if str =~ PLURAL
           str
         else