diff --git a/lib/btc/errors.js b/lib/btc/errors.js
index 7426180e..b38f4e66 100644
--- a/lib/btc/errors.js
+++ b/lib/btc/errors.js
@@ -7,6 +7,7 @@
 
 'use strict';
 
+var assert = require('assert');
 var util = require('../utils/util');
 var constants = require('../protocol/constants');
 var Amount = require('./amount');