diff --git a/src/Symfony/Component/Console/Output/ConsoleOutput.php b/src/Symfony/Component/Console/Output/ConsoleOutput.php
index 8e6821e5e3733..d71f062dfb62b 100644
--- a/src/Symfony/Component/Console/Output/ConsoleOutput.php
+++ b/src/Symfony/Component/Console/Output/ConsoleOutput.php
@@ -125,7 +125,7 @@ protected function hasStderrSupport()
      */
     private function isRunningOS400()
     {
-        return 'OS400' === php_uname('s');
+        return 'OS400' === PHP_OS;
     }
 
     /**