diff --git a/app/models/post_relation.rb b/app/models/post_relation.rb
index 1071234..336c8bd 100644
--- a/app/models/post_relation.rb
+++ b/app/models/post_relation.rb
@@ -72,8 +72,11 @@ class PostRelation < Array
   # Encuentra el primer post por el valor de un atributo
   # XXX: Acepta cualquier atributo
   def find_by(**args)
+    attr = args.first.first
+
     find_generic do |p|
-      p.public_send(args.first.first).try(:value) == args.first.last
+      p.attribute?(attr) &&
+        p.public_send(attr).value == args.first.last
     end
   end