diff --git a/web/src/render/index.html b/web/src/render/index.html
index e555720c..7a55f7f4 100644
--- a/web/src/render/index.html
+++ b/web/src/render/index.html
@@ -15,7 +15,9 @@
 
           if (!/Android|webOS|iPhone|iPad|iPod|BlackBerry/i.test(navigator.userAgent)) {
             width = width < PC_W ? width : PC_W
-            docEl.className += ' ispc-html'
+            if (!docEl.className.includes('ispc-html')) {
+              docEl.className += ' ispc-html'
+            }
           }
 
           var f = Math.min(width / 7.5, 50)