diff --git a/include/client/header.inc.php b/include/client/header.inc.php
index 8bbff83307e751f11a08d52c242858f5ce43c45d..5baea674254bc775d5c3cf7a1d0ad3ef3f5e6aa5 100644
--- a/include/client/header.inc.php
+++ b/include/client/header.inc.php
@@ -6,7 +6,7 @@ $signin_url = ROOT_PATH . "login.php"
 $signout_url = ROOT_PATH . "logout.php?auth=".$ost->getLinkToken();
 
 header("Content-Type: text/html; charset=UTF-8");
-header("Content-Security-Policy: frame-ancestors '".$cfg->getAllowIframes()."';");
+header("Content-Security-Policy: frame-ancestors ".$cfg->getAllowIframes().";");
 
 if (($lang = Internationalization::getCurrentLanguage())) {
     $langs = array_unique(array($lang, $cfg->getPrimaryLanguage()));