diff --git a/src/transaction.js b/src/transaction.js
index 4479577..90899b9 100644
--- a/src/transaction.js
+++ b/src/transaction.js
@@ -55,11 +55,16 @@ Transaction.prototype.addInput = function(tx, outIndex) {
   var hash
 
   if (typeof tx === 'string') {
-    hash = tx
+    hash = new Buffer(tx, 'hex')
+    assert.equal(hash.length, 32, 'Invalid TX hash')
+
+    // TxHash hex is big-endian, we need little-endian
+    Array.prototype.reverse.call(hash)
 
   } else {
-    assert(tx instanceof Transaction, 'Unexpected input: ' + tx)
-    hash = tx.getId()
+    assert(tx instanceof Transaction, 'Expected Transaction, got ' + tx)
+    hash = crypto.hash256(tx.toBuffer())
+
   }
 
   this.ins.push(new TransactionIn({
@@ -142,13 +147,8 @@ Transaction.prototype.toBuffer = function () {
   writeUInt32(this.version)
   writeVarInt(this.ins.length)
 
-  this.ins.forEach(function(txin) {
-    var hash = new Buffer(txin.outpoint.hash, 'hex') // FIXME: Performance: convert on tx.addInput instead
-
-    // TxHash hex is big-endian, we need little-endian
-    Array.prototype.reverse.call(hash)
-
-    writeSlice(hash)
+  this.ins.forEach(function(txin, i) {
+    writeSlice(txin.outpoint.hash)
     writeUInt32(txin.outpoint.index)
     writeVarInt(txin.script.buffer.length)
     writeSlice(txin.script.buffer)
@@ -240,9 +240,6 @@ Transaction.prototype.clone = function () {
 }
 
 Transaction.fromBuffer = function(buffer) {
-  // Copy because we mutate (reverse TxOutHashs)
-  buffer = new Buffer(buffer)
-
   var offset = 0
   function readSlice(n) {
     offset += n
@@ -272,10 +269,6 @@ Transaction.fromBuffer = function(buffer) {
 
   for (var i = 0; i < vinLen; ++i) {
     var hash = readSlice(32)
-
-    // TxHash is little-endian, we want big-endian hex
-    Array.prototype.reverse.call(hash)
-
     var vout = readUInt32()
     var scriptLen = readVarInt()
     var script = readSlice(scriptLen)
@@ -283,7 +276,7 @@ Transaction.fromBuffer = function(buffer) {
 
     ins.push(new TransactionIn({
       outpoint: {
-        hash: hash.toString('hex'),
+        hash: hash,
         index: vout
       },
       script: Script.fromBuffer(script),
diff --git a/src/wallet.js b/src/wallet.js
index 88d1695..4410b36 100644
--- a/src/wallet.js
+++ b/src/wallet.js
@@ -169,9 +169,15 @@ function Wallet(seed, network) {
       }
     })
 
-    tx.ins.forEach(function(txIn, i){
+    tx.ins.forEach(function(txIn, i) {
       var op = txIn.outpoint
-      var output = op.hash + ':' + op.index
+
+      // copy and convert to big-endian hex
+      var txinHash = new Buffer(op.hash)
+      Array.prototype.reverse.call(txinHash)
+      txinHash = txinHash.toString('hex')
+
+      var output = txinHash + ':' + op.index
 
       if(me.outputs[output]) delete me.outputs[output]
     })
diff --git a/test/bitcoin.core.js b/test/bitcoin.core.js
index b058385..48f594c 100644
--- a/test/bitcoin.core.js
+++ b/test/bitcoin.core.js
@@ -147,7 +147,12 @@ describe('Bitcoin-core', function() {
           var prevOutIndex = input[1]
   //          var prevOutScriptPubKey = input[2] // TODO: we don't have a ASM parser
 
-          assert.equal(txin.outpoint.hash, prevOutHash)
+          var actualHash = txin.outpoint.hash
+
+          // Test data is big-endian
+          Array.prototype.reverse.call(actualHash)
+
+          assert.equal(actualHash.toString('hex'), prevOutHash)
 
           // we read UInt32, not Int32
           assert.equal(txin.outpoint.index & 0xffffffff, prevOutIndex)
@@ -184,7 +189,7 @@ describe('Bitcoin-core', function() {
         }
 
         if (actualHash != undefined) {
-          // BigEndian test data
+          // Test data is big-endian
           Array.prototype.reverse.call(actualHash)
 
           assert.equal(actualHash.toString('hex'), expectedHash)
diff --git a/test/transaction.js b/test/transaction.js
index 78a5ca4..9bacec3 100644
--- a/test/transaction.js
+++ b/test/transaction.js
@@ -59,7 +59,7 @@ describe('Transaction', function() {
       assert.equal(input.sequence, 4294967295)
 
       assert.equal(input.outpoint.index, 0)
-      assert.equal(input.outpoint.hash, "69d02fc05c4e0ddc87e796eee42693c244a3112fffe1f762c3fb61ffcb304634")
+      assert.equal(input.outpoint.hash.toString('hex'), "344630cbff61fbc362f7e1ff2f11a344c29326e4ee96e787dc0d4e5cc02fd069")
 
       assert.equal(b2h(input.script.buffer),
                    "493046022100ef89701f460e8660c80808a162bbf2d676f40a331a243592c36d6bd1f81d6bdf022100d29c072f1b18e59caba6e1f0b8cadeb373fd33a25feded746832ec179880c23901")
@@ -120,7 +120,7 @@ describe('Transaction', function() {
         assert.equal(input.sequence, 4294967295)
 
         assert.equal(input.outpoint.index, 0)
-        assert.equal(input.outpoint.hash, "0cb859105100ebc3344f749c835c7af7d7103ec0d8cbc3d8ccbd5d28c3c36b57")
+        assert.equal(input.outpoint.hash.toString('hex'), "576bc3c3285dbdccd8c3cbd8c03e10d7f77a5c839c744f34c3eb00511059b80c")
 
         assert.equal(input.script, Script.EMPTY)
       }
diff --git a/test/wallet.js b/test/wallet.js
index cc8b760..7562bc5 100644
--- a/test/wallet.js
+++ b/test/wallet.js
@@ -14,7 +14,15 @@ var fixtureTx1Hex = fixtureTxes.prevTx
 var fixtureTx2Hex = fixtureTxes.tx
 
 function fakeTxHash(i) {
-  return "efefefefefefefefefefefefefefefefefefefefefefefefefefefefefefefe" + i
+  var hash = new Buffer(32)
+  hash.fill(i)
+  return hash
+}
+
+function fakeTxId(i) {
+  var hash = fakeTxHash(i)
+  Array.prototype.reverse.call(hash)
+  return hash.toString('hex')
 }
 
 describe('Wallet', function() {
@@ -263,12 +271,11 @@ describe('Wallet', function() {
     })
 
     describe('processConfirmedTx', function(){
-
       it('does not fail on scripts with no corresponding Address', function() {
         var pubKey = wallet.getPrivateKey(0).pub
         var script = scripts.pubKeyOutput(pubKey)
         var tx2 = new Transaction()
-        tx2.addInput(fakeTxHash(1), 0)
+        tx2.addInput(fakeTxId(1), 0)
 
         // FIXME: Transaction doesn't support custom ScriptPubKeys... yet
         // So for now, we hijack the script with our own, and undefine the cached address
@@ -365,19 +372,19 @@ describe('Wallet', function() {
       // set up 3 utxo
       utxo = [
         {
-          "hash": fakeTxHash(1),
+          "hash": fakeTxId(1),
           "outputIndex": 0,
           "address" : address1,
           "value": 400000 // not enough for value
         },
         {
-          "hash": fakeTxHash(2),
+          "hash": fakeTxId(2),
           "outputIndex": 1,
           "address" : address1,
           "value": 500000 // enough for only value
         },
         {
-          "hash": fakeTxHash(3),
+          "hash": fakeTxId(3),
           "outputIndex": 0,
           "address" : address2,
           "value": 520000 // enough for value and fee
@@ -415,7 +422,7 @@ describe('Wallet', function() {
       it('ignores pending outputs', function(){
         utxo.push(
           {
-            "hash": fakeTxHash(4),
+            "hash": fakeTxId(4),
             "outputIndex": 0,
             "address" : address2,
             "value": 530000,
@@ -437,7 +444,7 @@ describe('Wallet', function() {
         var address = wallet.generateAddress()
 
         wallet.setUnspentOutputs([{
-          hash: fakeTxHash(0),
+          hash: fakeTxId(0),
           outputIndex: 0,
           address: address,
           value: value
@@ -459,7 +466,7 @@ describe('Wallet', function() {
         var address = wallet.generateAddress()
 
         wallet.setUnspentOutputs([{
-          hash: fakeTxHash(0),
+          hash: fakeTxId(0),
           outputIndex: 0,
           address: address,
           value: value