diff --git a/client.inc.php b/client.inc.php
index bb8e8badbe7fdce1ef104276bff36448aa4126a6..64877cc46b004f2f9ef3d3a2c4c69a24b81f8b1d 100644
--- a/client.inc.php
+++ b/client.inc.php
@@ -48,7 +48,8 @@ $nav=null;
 $thisclient = UserAuthenticationBackend::getUser();
 
 if (isset($_GET['lang']) && $_GET['lang']) {
-    $_SESSION['client:lang'] = $_GET['lang'];
+    if (Internationalization::getLanguageInfo($_GET['lang']))
+        $_SESSION['client:lang'] = $_GET['lang'];
 }
 
 // Bootstrap gettext translations as early as possible, but after attempting