diff --git a/view/theme/vier/style.php b/view/theme/vier/style.php
index ac5cd08ef..8cd0d7a32 100644
--- a/view/theme/vier/style.php
+++ b/view/theme/vier/style.php
@@ -61,7 +61,7 @@ header('Cache-Control: public');
 header('ETag: "'.$etag.'"');
 header('Last-Modified: '.$modified);
 
-if (isset($_SERVER['HTTP_IF_MODIFIED_SINCE']) || isset($_SERVER['HTTP_IF_NONE_MATCH'])) {
+if (isset($_SERVER['HTTP_IF_MODIFIED_SINCE']) && isset($_SERVER['HTTP_IF_NONE_MATCH'])) {
 	$cached_modified = gmdate('r', strtotime($_SERVER['HTTP_IF_MODIFIED_SINCE']));
 	$cached_etag = str_replace(['"', "-gzip"], ['', ''],
 				stripslashes($_SERVER['HTTP_IF_NONE_MATCH']));