diff --git a/edit/match-highlighter-helper.js b/edit/match-highlighter-helper.js
index d1cd3d7e..08437dc0 100644
--- a/edit/match-highlighter-helper.js
+++ b/edit/match-highlighter-helper.js
@@ -225,6 +225,8 @@
     if (typeof needle === 'string') {
       return s.indexOf(needle);
     }
+    // FIXME: the current implementation will break when the highlighter addon
+    // is updated.
     const match = s.match(needle);
     return match ? match.index + match[1].length : -1;
   }