diff --git a/lib/bcoin/tx.js b/lib/bcoin/tx.js
index 5f1ddb38..1f74dc7b 100644
--- a/lib/bcoin/tx.js
+++ b/lib/bcoin/tx.js
@@ -655,73 +655,69 @@ TX.prototype.maxSize = function maxSize() {
   return size;
 };
 
-TX.prototype.utxos = function utxos(unspent) {
+TX.prototype.getUnspent = function getUnspent(unspent) {
+  var tx = this.clone();
+
   // NOTE: tx should be prefilled with all outputs
-  var cost = this.funds('out');
+  var cost = tx.funds('out');
 
   // Use initial fee for starters
   var fee = 1;
 
   // total = cost + fee
-  var total = cost.add(new bn(TX.fee));
+  var total = cost.addn(TX.fee);
 
-  var inputs = this.inputs.slice();
-  var utxos = [];
+  var inputs = [];
 
   var lastAdded = 0;
 
   var byteSize, addFee, change;
 
-  function addInput(unspent, i) {
+  function addInput(unspent) {
     // Add new inputs until TX will have enough funds to cover both
     // minimum post cost and fee
-    var index = this._input(unspent);
-    utxos.push(this.inputs[index]);
+    var index = tx._input(unspent);
+    inputs.push(tx.inputs[index]);
     lastAdded++;
-    return this.funds('in').cmp(total) < 0;
+    return tx.funds('in').cmp(total) < 0;
   }
 
   // Transfer `total` funds maximum
   // var unspent = wallet.unspent();
-  unspent.every(addInput, this);
+  unspent.every(addInput);
 
   // Add dummy output (for `change`) to calculate maximum TX size
-  this.output({ address: null, value: new bn(0) });
+  tx.output({ address: null, value: new bn(0) });
 
   // Change fee value if it is more than 1024 bytes
   // (10000 satoshi for every 1024 bytes)
   do {
     // Calculate maximum possible size after signing
-    byteSize = this.maxSize();
+    byteSize = tx.maxSize();
 
     addFee = Math.ceil(byteSize / 1024) - fee;
-    total.iadd(new bn(addFee * TX.fee));
+    total.iaddn(addFee * TX.fee);
     fee += addFee;
 
     // Failed to get enough funds, add more inputs
-    if (this.funds('in').cmp(total) < 0)
-      unspent.slice(lastAdded).every(addInput, this);
-  } while (this.funds('in').cmp(total) < 0 && lastAdded < unspent.length);
+    if (tx.funds('in').cmp(total) < 0)
+      unspent.slice(lastAdded).every(addInput);
+  } while (tx.funds('in').cmp(total) < 0 && lastAdded < unspent.length);
 
   // Still failing to get enough funds
-  if (this.funds('in').cmp(total) < 0) {
-    this.inputs = inputs;
+  if (tx.funds('in').cmp(total) < 0) {
     this.total = total;
-    this.outputs.pop();
     return null;
   }
 
   // How much money is left after sending outputs
-  change = this.funds('in').sub(total);
+  change = tx.funds('in').sub(total);
 
-  // Clear the tx of everything we added.
-  this.inputs = inputs;
   this.total = total;
-  this.outputs.pop();
 
-  // Return necessary utxos and change.
+  // Return necessary inputs and change.
   return {
-    utxos: utxos,
+    inputs: inputs,
     change: change,
     cost: cost,
     fee: total.sub(cost),
@@ -730,22 +726,25 @@ TX.prototype.utxos = function utxos(unspent) {
 };
 
 TX.prototype.fillUnspent = function fillUnspent(unspent, changeAddress) {
-  var result = unspent.utxos ? unspent : this.utxos(unspent);
-
-  this.changeAddress = changeAddress
-    || this.changeAddress
-    || utxos[0].output.addr;
+  var result = unspent.cost ? unspent : this.getUnspent(unspent);
 
   if (!result)
     return result;
 
-  result.utxos.forEach(function(input) {
+  this.changeAddress = changeAddress
+    || this.changeAddress
+    || result.inputs[0].output.addr;
+
+  result.inputs.forEach(function(input) {
     this.input(input);
   }, this);
 
   if (result.change.cmpn(TX.dust) < 0) {
     // Do nothing. Change is added to fee.
-    assert(this.getFee().cmp(result.fee.add(result.change)) === 0);
+    assert.equal(
+      this.getFee().toNumber(),
+      result.fee.add(result.change).toNumber()
+    );
     this.changeOutput = null;
   } else {
     if (!this.changeAddress)