From ea47cae003e7298cb91135645bb34fc0f57f860d Mon Sep 17 00:00:00 2001
From: gorhill <rhill@raymondhill.net>
Date: Tue, 9 May 2017 08:58:30 -0400
Subject: [PATCH] fix #2599

---
 src/js/static-net-filtering.js | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/src/js/static-net-filtering.js b/src/js/static-net-filtering.js
index a33f370ba..9f7c0d277 100644
--- a/src/js/static-net-filtering.js
+++ b/src/js/static-net-filtering.js
@@ -1443,10 +1443,13 @@ FilterParser.prototype.parse = function(raw) {
         s = s.slice(2);
 
         // convert hostname to punycode if needed
+        // https://github.com/gorhill/uBlock/issues/2599
         if ( this.reHasUnicode.test(s) ) {
             var matches = this.reIsolateHostname.exec(s);
             if ( matches ) {
-                s = matches[1] + punycode.toASCII(matches[2]) + matches[3];
+                s = (matches[1] !== undefined ? matches[1] : '') +
+                    punycode.toASCII(matches[2]) +
+                    matches[3];
                 //console.debug('µBlock.staticNetFilteringEngine/FilterParser.parse():', raw, '=', s);
             }
         }