diff --git a/api/thumbnail.php b/api/thumbnail.php
index d9ac47fb03..607ef57bdf 100644
--- a/api/thumbnail.php
+++ b/api/thumbnail.php
@@ -32,7 +32,7 @@ $GLOBALS['egw']->session->commit_session();
 
 if (!read_thumbnail(get_srcfile()))
 {
-	header('404 Not found');
+	http_response_code(404);   // Not found
 }
 
 /**
@@ -620,4 +620,4 @@ function gdVersion($user_ver = 0)
 	$info = stristr(ob_get_clean(), 'gd version');
 	if (preg_match('/\d/', $info, $match)) $gd_ver = $match[0];
 	return $match[0];
-}
+}
\ No newline at end of file