diff --git a/www/common/diffMarked.js b/www/common/diffMarked.js
index ddc0d0adf..71b2185ba 100644
--- a/www/common/diffMarked.js
+++ b/www/common/diffMarked.js
@@ -40,7 +40,7 @@ define([
                     Mermaid = _Mermaid;
                     Mermaid.initialize({
                         gantt: { axisFormat: '%m-%d', },
-                        theme: (window.CryptPad_theme === 'dark') ? 'dark' : undefined,
+                        theme: (window.CryptPad_theme === 'dark') ? 'dark' : 'default',
                         "themeCSS": mermaidThemeCSS,
                     });
                 }