diff --git a/src/Composer/Command/UpdateCommand.php b/src/Composer/Command/UpdateCommand.php
index d017097ee..e37109271 100644
--- a/src/Composer/Command/UpdateCommand.php
+++ b/src/Composer/Command/UpdateCommand.php
@@ -48,7 +48,7 @@ class UpdateCommand extends BaseCommand
                 new InputOption('dry-run', null, InputOption::VALUE_NONE, 'Outputs the operations but will not execute anything (implicitly enables --verbose).'),
                 new InputOption('dev', null, InputOption::VALUE_NONE, 'DEPRECATED: Enables installation of require-dev packages (enabled by default, only present for BC).'),
                 new InputOption('no-dev', null, InputOption::VALUE_NONE, 'Disables installation of require-dev packages.'),
-                new InputOption('lock', null, InputOption::VALUE_NONE, 'Only updates the lock file hash to suppress warning about the lock file being out of date.'),
+                new InputOption('lock', null, InputOption::VALUE_NONE, 'Updates the lock file hash to suppress warning about the lock file being out of date, and also updates the packages\' mirrors/URLs if they changed.'),
                 new InputOption('no-install', null, InputOption::VALUE_NONE, 'Skip the install step after updating the composer.lock file.'),
                 new InputOption('no-autoloader', null, InputOption::VALUE_NONE, 'Skips autoloader generation'),
                 new InputOption('no-scripts', null, InputOption::VALUE_NONE, 'Skips the execution of all scripts defined in composer.json file.'),