diff --git a/src/wp-includes/pomo/mo.php b/src/wp-includes/pomo/mo.php
index dcac16c6b3..6a14b04389 100644
--- a/src/wp-includes/pomo/mo.php
+++ b/src/wp-includes/pomo/mo.php
@@ -13,6 +13,11 @@ require_once __DIR__ . '/streams.php';
 if ( ! class_exists( 'MO', false ) ) :
 	class MO extends Gettext_Translations {
 
+		/**
+		 * Number of plural forms.
+		 *
+		 * @var int
+		 */
 		public $_nplurals = 2;
 
 		/**
diff --git a/src/wp-includes/pomo/translations.php b/src/wp-includes/pomo/translations.php
index 29ea11e45e..6a69ebdb3b 100644
--- a/src/wp-includes/pomo/translations.php
+++ b/src/wp-includes/pomo/translations.php
@@ -181,6 +181,21 @@ if ( ! class_exists( 'Translations', false ) ) :
 	}
 
 	class Gettext_Translations extends Translations {
+
+		/**
+		 * Number of plural forms.
+		 *
+		 * @var int
+		 */
+		public $_nplurals;
+
+		/**
+		 * Callback to retrieve the plural form.
+		 *
+		 * @var callable
+		 */
+		public $_gettext_select_plural_form;
+
 		/**
 		 * The gettext implementation of select_plural_form.
 		 *