diff --git a/src/wp-includes/plugin.php b/src/wp-includes/plugin.php
index ca4985f1f0..bdb9ebd17d 100644
--- a/src/wp-includes/plugin.php
+++ b/src/wp-includes/plugin.php
@@ -14,6 +14,8 @@
  * Also see the {@link https://codex.wordpress.org/Plugin_API Plugin API} for
  * more information and examples on how to use a lot of these functions.
  *
+ * This file should have no external dependencies.
+ *
  * @package WordPress
  * @subpackage Plugin
  * @since 1.5.0
diff --git a/src/wp-settings.php b/src/wp-settings.php
index dc3b25a7cb..7f136159c2 100644
--- a/src/wp-settings.php
+++ b/src/wp-settings.php
@@ -20,7 +20,7 @@ define( 'WPINC', 'wp-includes' );
 // Include files required for initialization.
 require( ABSPATH . WPINC . '/load.php' );
 require( ABSPATH . WPINC . '/default-constants.php' );
-require( ABSPATH . WPINC . '/plugin.php' );
+require_once( ABSPATH . WPINC . '/plugin.php' );
 
 /*
  * These can't be directly globalized in version.php. When updating,