diff --git a/src/Symfony/Component/Process/Process.php b/src/Symfony/Component/Process/Process.php
index ac79bbb6ae..7e941c9cb3 100644
--- a/src/Symfony/Component/Process/Process.php
+++ b/src/Symfony/Component/Process/Process.php
@@ -50,6 +50,8 @@ class Process
     /**
      * Exit codes translation table.
      *
+     * User-defined errors must use exit codes in the 64-113 range.
+     *
      * @var array
      */
     static public $exitCodes = array(