Index: src/wp-admin/includes/plugin.php
===================================================================
--- src/wp-admin/includes/plugin.php	(revision 28624)
+++ src/wp-admin/includes/plugin.php	(working copy)
@@ -538,7 +538,9 @@
 			wp_redirect(add_query_arg('_error_nonce', wp_create_nonce('plugin-activation-error_' . $plugin), $redirect)); // we'll override this later if the plugin can be included without fatal error
 		ob_start();
 		wp_register_plugin_realpath( WP_PLUGIN_DIR . '/' . $plugin );
+		$_wp_plugin_file = $plugin;
 		include_once( WP_PLUGIN_DIR . '/' . $plugin );
+		$plugin = $_wp_plugin_file; // Avoid stomping of the $plugin variable in a plugin.
 
 		if ( ! $silent ) {
 			/**