diff --git a/lib/bcoin/utils.js b/lib/bcoin/utils.js
index 737ffdc8..f91b540a 100644
--- a/lib/bcoin/utils.js
+++ b/lib/bcoin/utils.js
@@ -326,7 +326,7 @@ utils.asyncify = function asyncify(fn) {
   };
 };
 
-utils.revHex = function revHex() {
+utils.revHex = function revHex(s) {
   var r = '';
   for (var i = 0; i < s.length; i += 2)
     r = s.slice(i, i + 2) + r;