diff --git a/index.js b/index.js
index <HASH>..<HASH> 100644
--- a/index.js
+++ b/index.js
@@ -41,6 +41,6 @@ module.exports = function createGenerator(pattern, options) {
     var genericName = interpolateName(loaderContext, name, loaderOptions);
     return genericName
       .replace(new RegExp('[^a-zA-Z0-9\\-_\u00A0-\uFFFF]', 'g'), '-')
-      .replace(/^([^a-zA-Z_])/, '_$1');
+      .replace(/^((-?[0-9])|--)/, "_$1");
   };
 };
Prefix hashes with underscores based on CSS spec

To match with <URL>