diff --git a/src/transaction_builder.js b/src/transaction_builder.js
index e2b7e28..a08af72 100644
--- a/src/transaction_builder.js
+++ b/src/transaction_builder.js
@@ -1,4 +1,5 @@
 var assert = require('assert')
+var bufferutils = require('./bufferutils')
 var ops = require('./opcodes')
 var scripts = require('./scripts')