diff --git a/src/core/render/slugify.js b/src/core/render/slugify.js
index c6bda03d..1d3c24b3 100644
--- a/src/core/render/slugify.js
+++ b/src/core/render/slugify.js
@@ -18,7 +18,8 @@ export function slugify(str) {
     .replace(/<[^>\d]+>/g, '')
     .replace(re, '')
     .replace(/\s/g, '-')
-    .replace(/-+/g, '-');
+    .replace(/-+/g, '-')
+    .replace(/^(\d)/, '_$1');
   let count = cache[slug];
 
   count = hasOwn.call(cache, slug) ? count + 1 : 0;