diff --git a/lib/remark-sub.js b/lib/remark-sub.js
index d3138a54..2e608664 100644
--- a/lib/remark-sub.js
+++ b/lib/remark-sub.js
@@ -1,6 +1,6 @@
 import findAndReplace from 'mdast-util-find-and-replace'
 
-const subGroup = '[\\w_]+'
+const subGroup = '[A-Za-z][\\w_]+'
 
 const subRegex = new RegExp(
   '~(' + subGroup + '(?:\\/' + subGroup + ')?)',