diff --git a/app/controllers/api/v1/sites_controller.rb b/app/controllers/api/v1/sites_controller.rb
index 384a8e4f..f13376fa 100644
--- a/app/controllers/api/v1/sites_controller.rb
+++ b/app/controllers/api/v1/sites_controller.rb
@@ -6,6 +6,8 @@ module Api
     class SitesController < BaseController
       http_basic_authenticate_with name: ENV['HTTP_BASIC_USER'],
                                    password: ENV['HTTP_BASIC_PASSWORD']
+      SUBDOMAIN = ".#{Site.domain}"
+      PARTS = Site.domain.split('.').count
 
       # Lista de nombres de dominios a emitir certificados
       def index
@@ -24,13 +26,17 @@ module Api
         name.end_with?('.') ? name[0..-2] : "#{name}.#{Site.domain}"
       end
 
+      # Es un subdominio directo del dominio principal
+      #
+      # @param name [String]
+      # @return [Bool]
       def subdomain?(name)
-        @@subdomain ||= ".#{Site.domain}"
-
-        name.end_with? @subdomain
+        name.end_with?(SUBDOMAIN) && name.split('.').count == (PARTS + 1)
       end
 
       # Dominios alternativos
+      #
+      # @return [Array<String>]
       def alternative_names
         hostname_of(DeployAlternativeDomain.all).concat(hostname_of(DeployLocalizedDomain)).map do |name|
           canonicalize name
@@ -41,6 +47,8 @@ module Api
 
       # Obtener todos los sitios con API habilitada, es decir formulario
       # de contacto y/o colaboración anónima.
+      #
+      # @return [Array<String>]
       def api_names
         Site.where(contact: true)
             .or(Site.where(colaboracion_anonima: true))