Index: src/wp-settings.php
===================================================================
--- src/wp-settings.php	(revision 52957)
+++ src/wp-settings.php	(working copy)
@@ -346,7 +346,9 @@
 
 // Load must-use plugins.
 foreach ( wp_get_mu_plugins() as $mu_plugin ) {
+	$_wp_plugin_file = $mu_plugin;
 	include_once $mu_plugin;
+	$mu_plugin = $_wp_plugin_file; // Avoid stomping of the $mu_plugin variable in a plugin.
 
 	/**
 	 * Fires once a single must-use plugin has loaded.
@@ -357,13 +359,16 @@
 	 */
 	do_action( 'mu_plugin_loaded', $mu_plugin );
 }
-unset( $mu_plugin );
+unset( $mu_plugin, $_wp_plugin_file );
 
 // Load network activated plugins.
 if ( is_multisite() ) {
 	foreach ( wp_get_active_network_plugins() as $network_plugin ) {
 		wp_register_plugin_realpath( $network_plugin );
+
+		$_wp_plugin_file = $network_plugin;
 		include_once $network_plugin;
+		$network_plugin = $_wp_plugin_file; // Avoid stomping of the $network_plugin variable in a plugin.
 
 		/**
 		 * Fires once a single network-activated plugin has loaded.
@@ -374,7 +379,7 @@
 		 */
 		do_action( 'network_plugin_loaded', $network_plugin );
 	}
-	unset( $network_plugin );
+	unset( $network_plugin, $_wp_plugin_file );
 }
 
 /**
@@ -415,7 +420,10 @@
 // Load active plugins.
 foreach ( wp_get_active_and_valid_plugins() as $plugin ) {
 	wp_register_plugin_realpath( $plugin );
+
+	$_wp_plugin_file = $plugin;
 	include_once $plugin;
+	$plugin = $_wp_plugin_file; // Avoid stomping of the $plugin variable in a plugin.
 
 	/**
 	 * Fires once a single activated plugin has loaded.
@@ -426,7 +434,7 @@
 	 */
 	do_action( 'plugin_loaded', $plugin );
 }
-unset( $plugin );
+unset( $plugin, $_wp_plugin_file );
 
 // Load pluggable functions.
 require ABSPATH . WPINC . '/pluggable.php';