diff --git a/lib/crypto/MGF1.js b/lib/crypto/MGF1.js
index d68a691..0a7aeed 100644
--- a/lib/crypto/MGF1.js
+++ b/lib/crypto/MGF1.js
@@ -1,13 +1,13 @@
 'use strict';
 
 const crypto = require('crypto');
-const BN = require('bn.js');
+
+const BigNumber = require('../BigNumber.js');
 
 const MFG_LEN = 32;
 
 const divceil = (a, b) => ~~(((a + b) - 1) / b); // eslint-disable-line no-bitwise
-const rjust = (string, width, padding) => {
-	padding = padding || ' ';
+const rjust = (string, width, padding = ' ') => {
 	padding = padding.substr(0, 1);
 	if (string.length < width)
 		return padding.repeat(width - string.length) + string;
@@ -26,7 +26,7 @@ const i2osp = (x, len) => {
 	if (x >= 256 ** len)
 		throw new Error('Integer too large');
 
-	return Buffer.from(rjust((Buffer.from((new BN(x)).toArray('be', 4)).toString()).replace(/\x00/gi, ''), len, '\x00')); // eslint-disable-line no-control-regex
+	return Buffer.from(rjust(new BigNumber(x).toBEBuffer(4).toString().replace(/\x00/gi, ''), len, '\x00')); // eslint-disable-line no-control-regex
 };
 
 module.exports = {