diff --git a/doc/rpm-build/post_install.php b/doc/rpm-build/post_install.php
index 15822330ed..3869d729a9 100755
--- a/doc/rpm-build/post_install.php
+++ b/doc/rpm-build/post_install.php
@@ -69,7 +69,7 @@ $config = array(
 );
 
 // read language from LANG enviroment variable
-if (($lang = isset($_ENV['LANG']) ? $_ENV['LANG'] : $_SERVER['LANG']))
+if (($lang = isset($_ENV['LANG']) ? $_ENV['LANG'] : (isset($_SERVER['LANG']) ? $_SERVER['LANG'] : null)))
 {
 	@list($lang,$nat) = preg_split('/[_.]/',$lang);
 	if (in_array($lang.'-'.strtolower($nat),array('es-es','pt-br','zh-tw')))