diff --git a/lib/errors/spec.js b/lib/errors/spec.js
index c2dd28a..eece532 100644
--- a/lib/errors/spec.js
+++ b/lib/errors/spec.js
@@ -72,6 +72,15 @@ module.exports = [{
   }, {
     name: 'ChangeAddressMissing',
     message: 'Change address is missing'
+  }, {
+    name: 'BlockHeightTooHigh',
+    message: 'Block Height can be at most 2^32 -1'
+  }, {
+    name: 'NLockTimeOutOfRange',
+    message: 'Block Height can only be between 0 and 499 999 999'
+  }, {
+    name: 'LockTimeTooEarly',
+    message: 'Lock Time can\'t be earlier than UNIX date 500 000 000'
   }]
 }, {
   name: 'Script',
diff --git a/lib/transaction/transaction.js b/lib/transaction/transaction.js
index 74e06fb..ef28e0a 100644
--- a/lib/transaction/transaction.js
+++ b/lib/transaction/transaction.js
@@ -66,6 +66,12 @@ function Transaction(serialized) {
 // max amount of satoshis in circulation
 Transaction.MAX_MONEY = 21000000 * 1e8;
 
+// nlocktime limit to be considered block height rather than a timestamp
+Transaction.NLOCKTIME_BLOCKHEIGHT_LIMIT = 5e8;
+
+// Max value for an unsigned 32 bit value 
+Transaction.NLOCKTIME_MAX_VALUE = 4294967295;
+
 /* Constructors and Serialization */
 
 /**
@@ -280,13 +286,41 @@ Transaction.prototype.fromObject = function(transaction) {
 };
 
 /**
- * sets nLockTime so that transaction is not valid until 
- * the desired date or block height
+ * Sets nLockTime so that transaction is not valid until the desired date(a
+ * timestamp in seconds since UNIX epoch is also accepted)
+ *
  * @param {Date | Number} time  
+ * @return {Transaction} this
  */
-Transaction.prototype.lockUntil = function(time) {
+Transaction.prototype.lockUntilDate = function(time) {
   $.checkArgument(time);
-  this.nLockTime = DEFAULT_NLOCKTIME;
+  if (_.isNumber(time) && time < Transaction.NLOCKTIME_BLOCKHEIGHT_LIMIT) {
+    throw new errors.Transaction.LockTimeTooEarly();
+  }
+  if (_.isDate(time)) {
+    time = time.getTime() / 1000;
+  }
+  this.nLockTime = time;
+  return this;
+};
+
+/**
+ * Sets nLockTime so that transaction is not valid until the desired block
+ * height.
+ *
+ * @param {Number} time  
+ * @return {Transaction} this
+ */
+Transaction.prototype.lockUntilBlockHeight = function(time) {
+  $.checkArgument(_.isNumber(time));
+  if (time >= Transaction.NLOCKTIME_BLOCKHEIGHT_LIMIT) {
+    throw new errors.Transaction.BlockHeightTooHigh();
+  }
+  if (time < 0) {
+    throw new errors.Transaction.NLockTimeOutOfRange();
+  }
+  this.nLockTime = time;
+  return this;
 };
 
 Transaction.prototype.toJSON = function toJSON() {
diff --git a/test/transaction/transaction.js b/test/transaction/transaction.js
index dbbd348..56bbee1 100644
--- a/test/transaction/transaction.js
+++ b/test/transaction/transaction.js
@@ -407,6 +407,46 @@ describe('Transaction', function() {
       transaction.outputs.length.should.equal(1);
     });
   });
+
+  describe.only('setting the nLockTime', function() {
+    var MILLIS_IN_SECOND = 1000;
+    var timestamp = 1423504946;
+    var blockHeight = 342734;
+    var date = new Date(timestamp * MILLIS_IN_SECOND);
+    it('accepts a date instance', function() {
+      var transaction = new Transaction()
+        .lockUntilDate(date);
+      transaction.nLockTime.should.equal(timestamp);
+    });
+    it('accepts a number instance with a timestamp', function() {
+      var transaction = new Transaction()
+        .lockUntilDate(timestamp);
+      transaction.nLockTime.should.equal(timestamp);
+    });
+    it('accepts a block height', function() {
+      var transaction = new Transaction()
+        .lockUntilBlockHeight(blockHeight);
+      transaction.nLockTime.should.equal(blockHeight);
+    });
+    it('fails if the block height is too high', function() {
+      expect(function() {
+        return new Transaction().lockUntilBlockHeight(5e8);
+      }).to.throw(errors.Transaction.BlockHeightTooHigh);
+    });
+    it('fails if the date is too early', function() {
+      expect(function() {
+        return new Transaction().lockUntilDate(1);
+      }).to.throw(errors.Transaction.LockTimeTooEarly);
+      expect(function() {
+        return new Transaction().lockUntilDate(499999999);
+      }).to.throw(errors.Transaction.LockTimeTooEarly);
+    });
+    it('fails if the date is negative', function() {
+      expect(function() {
+        return new Transaction().lockUntilBlockHeight(-1);
+      }).to.throw(errors.Transaction.NLockTimeOutOfRange);
+    });
+  });
 });
 
 var tx_empty_hex = '01000000000000000000';