diff --git a/src/transaction.js b/src/transaction.js
index 0195067..f061c77 100644
--- a/src/transaction.js
+++ b/src/transaction.js
@@ -39,15 +39,17 @@ Transaction.prototype.addInput = function(tx, index, sequence) {
 
   if (typeof tx === 'string') {
     hash = new Buffer(tx, 'hex')
-    assert.equal(hash.length, 32, 'Expected Transaction or string, got ' + tx)
+    assert.equal(hash.length, 32, 'Expected Transaction, txId or txHash, got ' + tx)
 
-    // TxHash hex is big-endian, we need little-endian
+    // TxId hex is big-endian, we need little-endian
     Array.prototype.reverse.call(hash)
 
-  } else {
-    assert(tx instanceof Transaction, 'Expected Transaction or string, got ' + tx)
-    hash = crypto.hash256(tx.toBuffer())
+  } else if (tx instanceof Transaction) {
+    hash = tx.getHash()
 
+  } else {
+    assert(Buffer.isBuffer(tx), 'Expected Transaction, txId or txHash, got ' + tx)
+    hash = tx
   }
 
   assert.equal(typeof index, 'number', 'Expected number index, got ' + index)
diff --git a/test/transaction.js b/test/transaction.js
index 0ebf50a..a7e08c1 100644
--- a/test/transaction.js
+++ b/test/transaction.js
@@ -69,6 +69,13 @@ describe('Transaction', function() {
       assert.deepEqual(tx.ins[0].hash, prevTxHash)
     })
 
+    it('accepts a transaction hash', function() {
+      var tx = new Transaction()
+      tx.addInput(prevTxHash, 0)
+
+      assert.deepEqual(tx.ins[0].hash, prevTxHash)
+    })
+
     it('accepts a Transaction object', function() {
       var tx = new Transaction()
       tx.addInput(prevTx, 0)
@@ -78,13 +85,13 @@ describe('Transaction', function() {
 
     it('returns an index', function() {
       var tx = new Transaction()
-      assert.equal(tx.addInput(prevTxId, 0), 0)
-      assert.equal(tx.addInput(prevTxId, 0), 1)
+      assert.equal(tx.addInput(prevTxHash, 0), 0)
+      assert.equal(tx.addInput(prevTxHash, 0), 1)
     })
 
     it('defaults to DEFAULT_SEQUENCE', function() {
       var tx = new Transaction()
-      tx.addInput(prevTxId, 0)
+      tx.addInput(prevTxHash, 0)
 
       assert.equal(tx.ins[0].sequence, 0xffffffff)
     })
@@ -94,11 +101,7 @@ describe('Transaction', function() {
         var tx = new Transaction()
 
         f.raw.ins.forEach(function(txIn, i) {
-          var txInId = new Buffer(txIn.hash)
-          Array.prototype.reverse.call(txInId)
-          txInId = txInId.toString('hex')
-
-          var j = tx.addInput(txInId, txIn.index, txIn.sequence)
+          var j = tx.addInput(txIn.hash, txIn.index, txIn.sequence)
 
           assert.equal(i, j)
           assert.deepEqual(tx.ins[i].hash, txIn.hash)