Index: src/wp-includes/plugin.php
===================================================================
--- src/wp-includes/plugin.php	(revision 44492)
+++ src/wp-includes/plugin.php	(working copy)
@@ -726,6 +726,18 @@
 }
 
 /**
+ * Load plugin main file.
+ *
+ * Using a function prevents global variable created in the plugin main file.
+ *
+ * @param  string $file Known path to the file.
+ * @return void
+ */
+function wp_load_plugin( $file ) {
+	include_once( $file );
+}
+
+/**
  * Get the filesystem directory path (with trailing slash) for the plugin __FILE__ passed in.
  *
  * @since 2.8.0
Index: src/wp-settings.php
===================================================================
--- src/wp-settings.php	(revision 44492)
+++ src/wp-settings.php	(working copy)
@@ -275,7 +275,7 @@
 
 // Load must-use plugins.
 foreach ( wp_get_mu_plugins() as $mu_plugin ) {
-	include_once( $mu_plugin );
+	wp_load_plugin( $mu_plugin );
 
 	/**
 	 * Fires once a single must-use plugin has loaded.
@@ -292,7 +292,7 @@
 if ( is_multisite() ) {
 	foreach ( wp_get_active_network_plugins() as $network_plugin ) {
 		wp_register_plugin_realpath( $network_plugin );
-		include_once( $network_plugin );
+		wp_load_plugin( $network_plugin );
 
 		/**
 		 * Fires once a single network-activated plugin has loaded.
@@ -339,7 +339,7 @@
 // Load active plugins.
 foreach ( wp_get_active_and_valid_plugins() as $plugin ) {
 	wp_register_plugin_realpath( $plugin );
-	include_once( $plugin );
+	wp_load_plugin( $plugin );
 
 	/**
 	 * Fires once a single activated plugin has loaded.