diff --git a/inc/parser/xhtml.php b/inc/parser/xhtml.php
index b6cc49cba9ae3feacada89a5d78937edc11653aa..2638cb24017d957a1d12685669c45a864feadd8c 100644
--- a/inc/parser/xhtml.php
+++ b/inc/parser/xhtml.php
@@ -186,7 +186,7 @@ class Doku_Renderer_xhtml extends Doku_Renderer {
     }
 
     function section_open($level) {
-        $this->doc .= "<div class='level$level'>".DOKU_LF;
+        $this->doc .= '<div class="level' . $level . '">' . DOKU_LF;
     }
 
     function section_close() {