diff --git a/lib/privatekey.js b/lib/privatekey.js
index 48f132e26..d445b530b 100644
--- a/lib/privatekey.js
+++ b/lib/privatekey.js
@@ -353,8 +353,7 @@ PrivateKey.prototype.toBigNumber = function () {
  * @returns {Buffer} A buffer of the private key
  */
 PrivateKey.prototype.toBuffer = function () {
-  // TODO: use `return this.bn.toBuffer({ size: 32 })` in v1.0.0
-  return this.bn.toBuffer();
+  return this.bn.toBuffer({ size: 32 });
 };
 
 /**