diff --git a/lib/TransactionBuilder.js b/lib/TransactionBuilder.js
index 73688c4..263e49c 100644
--- a/lib/TransactionBuilder.js
+++ b/lib/TransactionBuilder.js
@@ -231,7 +231,7 @@ TransactionBuilder.prototype._selectUnspent = function(neededAmountSat) {
   if (this.spendUnconfirmed) minConfirmationSteps.push(0);
 
   var sel = [],
-    totalSat = new bignum(0),
+    totalSat = bignum(0),
     fulfill = false,
     maxConfirmations = null,
     l = this.utxos.length;
@@ -246,9 +246,9 @@ TransactionBuilder.prototype._selectUnspent = function(neededAmountSat) {
         continue;
 
       var sat = u.amountSat || util.parseValue(u.amount);
-      totalSat = totalSat.add(new bignum(sat));
+      totalSat = totalSat.add(sat);
       sel.push(u);
-      if (totalSat.cmp(new bignum(neededAmountSat)) >= 0) {
+      if (totalSat.cmp(neededAmountSat) >= 0) {
         fulfill = true;
         break;
       }
@@ -268,11 +268,11 @@ TransactionBuilder.prototype._selectUnspent = function(neededAmountSat) {
 TransactionBuilder.prototype._setInputs = function(txobj) {
   var ins = this.selectedUtxos;
   var l = ins.length;
-  var valueInSat = new bignum(0);
+  var valueInSat = bignum(0);
 
   txobj.ins = [];
   for (var i = 0; i < l; i++) {
-    valueInSat = valueInSat.add(new bignum(util.parseValue(ins[i].amount)));
+    valueInSat = valueInSat.add(util.parseValue(ins[i].amount));
 
     var txin = {};
     txin.s = util.EMPTY_BUFFER;
@@ -297,9 +297,9 @@ TransactionBuilder.prototype._setFee = function(feeSat) {
     throw new Error('valueOutSat undefined');
 
 
-  var valueOutSat = this.valueOutSat.add(new bignum(feeSat));
+  var valueOutSat = this.valueOutSat.add(feeSat);
 
-  if (this.valueInSat.cmp(new bignum(valueOutSat)) < 0) {
+  if (this.valueInSat.cmp(valueOutSat) < 0) {
     var inv = this.valueInSat.toString();
     var ouv = valueOutSat.toString();
     throw new Error('transaction input amount is less than outputs: ' +
@@ -316,16 +316,16 @@ TransactionBuilder.prototype._setRemainder = function(txobj, remainderIndex) {
     throw new Error('valueInSat / valueOutSat undefined');
 
   /* add remainder (without modifying outs[]) */
-  var remainderSat = this.valueInSat.sub(new bignum(this.valueOutSat)).sub(new bignum(this.feeSat));
+  var remainderSat = this.valueInSat.sub(this.valueOutSat).sub(this.feeSat);
   var l = txobj.outs.length;
-  this.remainderSat = new bignum(0);
+  this.remainderSat = bignum(0);
 
   /*remove old remainder? */
   if (l > remainderIndex) {
     txobj.outs.pop();
   }
 
-  if (remainderSat.cmp(new bignum(0)) > 0) {
+  if (remainderSat.cmp(0) > 0) {
     var remainderOut = this.remainderOut || this.selectedUtxos[0];
     var value = util.bigIntToValue(remainderSat);
     var script = TransactionBuilder._scriptForOut(remainderOut);
@@ -352,7 +352,7 @@ TransactionBuilder.prototype._setFeeAndRemainder = function(txobj) {
     var feeSat = this.givenFeeSat ?
       this.givenFeeSat : maxSizeK * FEE_PER_1000B_SAT;
 
-    var neededAmountSat = this.valueOutSat.add(new bignum(feeSat));
+    var neededAmountSat = this.valueOutSat.add(feeSat);
 
     this._selectUnspent(neededAmountSat)
       ._setInputs(txobj)
@@ -381,7 +381,7 @@ TransactionBuilder.prototype._setFeeAndRemainder = function(txobj) {
 //
 
 TransactionBuilder.prototype.setOutputs = function(outs) {
-  var valueOutSat = new bignum(0);
+  var valueOutSat = bignum(0);
 
   var txobj = {};
   txobj.version = 1;
@@ -401,7 +401,7 @@ TransactionBuilder.prototype.setOutputs = function(outs) {
     txobj.outs.push(txout);
 
     var sat = outs[i].amountSat || util.parseValue(outs[i].amount);
-    valueOutSat = valueOutSat.add(new bignum(sat));
+    valueOutSat = valueOutSat.add(sat);
   }
 
   this.valueOutSat = valueOutSat;