Index: src/wp-admin/includes/plugin.php
===================================================================
--- src/wp-admin/includes/plugin.php	(revision 27080)
+++ src/wp-admin/includes/plugin.php	(working copy)
@@ -920,7 +920,9 @@
 		}
 		unset($uninstallable_plugins);

-		define('WP_UNINSTALL_PLUGIN', $file);
+		if ( ! defined( 'WP_UNINSTALL_PLUGIN' ) ) {
+			define( 'WP_UNINSTALL_PLUGIN', true );
+		}
 		include WP_PLUGIN_DIR . '/' . dirname($file) . '/uninstall.php';

 		return true;