diff --git a/index.js b/index.js
index 0c874ea..58acda0 100644
--- a/index.js
+++ b/index.js
@@ -3,7 +3,7 @@
 exports.Client = Client
 exports.Server = Server
 
-var bn = require('bn.js')
+var BN = require('bn.js')
 var bncode = require('bncode')
 var compact2string = require('compact2string')
 var dgram = require('dgram')
@@ -71,7 +71,7 @@ Tracker.prototype.complete = function (opts) {
   var self = this
   opts = opts || {}
   opts.event = 'completed'
-  opts.downloaded = self._torrentLength
+  opts.downloaded = opts.downloaded || self.torrentLength || 0
   self._request(opts)
 }
 
@@ -126,13 +126,16 @@ Tracker.prototype._request = function (opts) {
     info_hash: bytewiseEncodeURIComponent(self.client._infoHash),
     peer_id: bytewiseEncodeURIComponent(self.client._peerId),
     port: self.client._port,
-    left: self.client._torrentLength - (opts.downloaded || 0),
     compact: 1,
     numwant: self.client._numWant,
     uploaded: 0, // default, user should provide real value
     downloaded: 0 // default, user should provide real value
   }, opts)
 
+  if (self.client.torrentLength !== undefined) {
+    opts.left = self.client.torrentLength - (opts.downloaded || 0)
+  }
+
   if (self._trackerId) {
     opts.trackerid = self._trackerId
   }
@@ -267,7 +270,7 @@ Tracker.prototype._requestUdp = function (requestUrl, opts) {
       self.client._infoHash,
       self.client._peerId,
       toUInt64(opts.downloaded || 0),
-      toUInt64(opts.left || 0),
+      opts.left ? toUInt64(opts.left) : new Buffer('FFFFFFFFFFFFFFFF', 'hex'),
       toUInt64(opts.uploaded || 0),
       toUInt32(EVENTS[opts.event] || 0),
       toUInt32(0), // ip address (optional)
@@ -390,13 +393,17 @@ function Client (peerId, port, torrent, opts) {
   self._infoHash = Buffer.isBuffer(torrent.infoHash)
     ? torrent.infoHash
     : new Buffer(torrent.infoHash, 'hex')
-  self._torrentLength = torrent.length
+  self.torrentLength = torrent.length
   self._announce = torrent.announce
 
   // optional
   self._numWant = self._opts.numWant || 80
   self._intervalMs = self._opts.interval || (30 * 60 * 1000) // default: 30 minutes
 
+  if (typeof torrent.announce === 'string') {
+    // magnet-uri returns a string if the magnet uri only contains one 'tr' parameter
+    torrent.announce = [torrent.announce]
+  }
   self._trackers = torrent.announce.map(function (announceUrl) {
     return new Tracker(self, announceUrl, self._opts)
   })
@@ -700,7 +707,7 @@ function toUInt32 (n) {
 
 function toUInt64 (n) {
   if (n > MAX_UINT || typeof n === 'string') {
-    var bytes = bn(n).toArray()
+    var bytes = new BN(n).toArray()
     while (bytes.length < 8) {
       bytes.unshift(0)
     }
diff --git a/package.json b/package.json
index 549fcfe..c127343 100644
--- a/package.json
+++ b/package.json
@@ -1,7 +1,7 @@
 {
   "name": "bittorrent-tracker",
   "description": "Simple, robust, BitTorrent tracker (client & server) implementation",
-  "version": "0.6.0",
+  "version": "0.7.0",
   "author": {
     "name": "Feross Aboukhadijeh",
     "email": "feross@feross.org",
@@ -19,9 +19,10 @@
     "querystring": "^0.2.0",
     "run-parallel": "^1.0.0",
     "string2compact": "^1.1.0",
-    "bn.js": "^0.3.1"
+    "bn.js": "^0.4.3"
   },
   "devDependencies": {
+    "magnet-uri": "^2.0.1",
     "parse-torrent": "^1.1.0",
     "portfinder": "^0.2.1",
     "tape": "2.x"
diff --git a/test/client-large-torrent.js b/test/client-large-torrent.js
index 62c5f03..c21950b 100644
--- a/test/client-large-torrent.js
+++ b/test/client-large-torrent.js
@@ -11,7 +11,7 @@ var port = 6881
 // remove all tracker servers except a single UDP one, for now
 parsedTorrent.announce = [ 'udp://tracker.publicbt.com:80/announce' ]
 
-test('client.start()', function (t) {
+test('large torrent: client.start()', function (t) {
   t.plan(4)
 
   var client = new Client(peerId, port, parsedTorrent)
diff --git a/test/client-magnet.js b/test/client-magnet.js
new file mode 100644
index 0000000..e5bcd83
--- /dev/null
+++ b/test/client-magnet.js
@@ -0,0 +1,50 @@
+var Client = require('../').Client
+var fs = require('fs')
+var magnet = require('magnet-uri')
+var test = require('tape')
+
+var uri = 'magnet:?xt=urn:btih:d2474e86c95b19b8bcfdb92bc12c9d44667cfa36&dn=Leaves+of+Grass+by+Walt+Whitman.epub&tr=udp%3A%2F%2Ftracker.openbittorrent.com%3A80'
+var parsedTorrent = magnet(uri)
+var peerId = new Buffer('01234567890123456789')
+var announceUrl = 'udp://tracker.openbittorrent.com:80' // TODO: shouldn't rely on an external server!
+var port = 6881
+
+test('magnet + udp: client.start/update/stop()', function (t) {
+  t.plan(10)
+
+  var client = new Client(peerId, port, parsedTorrent)
+
+  client.on('error', function (err) {
+    t.error(err)
+  })
+
+  client.once('update', function (data) {
+    t.equal(data.announce, announceUrl)
+    t.equal(typeof data.complete, 'number')
+    t.equal(typeof data.incomplete, 'number')
+  })
+
+  client.once('peer', function (addr) {
+    t.pass('there is at least one peer') // TODO: this shouldn't rely on an external server!
+
+    client.once('update', function (data) {
+      // receive one final update after calling stop
+      t.equal(data.announce, announceUrl)
+      t.equal(typeof data.complete, 'number')
+      t.equal(typeof data.incomplete, 'number')
+
+      client.once('update', function (data) {
+        // received an update!
+        t.equal(data.announce, announceUrl)
+        t.equal(typeof data.complete, 'number')
+        t.equal(typeof data.incomplete, 'number')
+      })
+
+      client.stop()
+    })
+
+    client.update()
+  })
+
+  client.start()
+})
diff --git a/test/client.js b/test/client.js
index 43b910e..5215e2d 100644
--- a/test/client.js
+++ b/test/client.js
@@ -3,13 +3,15 @@ var fs = require('fs')
 var parseTorrent = require('parse-torrent')
 var test = require('tape')
 
+// TODO: add test where tracker doesn't support compact
+
 var torrent = fs.readFileSync(__dirname + '/torrents/bitlove-intro.torrent')
 var parsedTorrent = parseTorrent(torrent)
 var peerId = new Buffer('01234567890123456789')
 var announceUrl = 'http://t.bitlove.org/announce' // TODO: shouldn't rely on an external server!
 var port = 6881
 
-test('client.start()', function (t) {
+test('torrent: client.start()', function (t) {
   t.plan(4)
 
   var client = new Client(peerId, port, parsedTorrent)
@@ -32,7 +34,7 @@ test('client.start()', function (t) {
   client.start()
 })
 
-test('client.stop()', function (t) {
+test('torrent: client.stop()', function (t) {
   t.plan(4)
 
   var client = new Client(peerId, port, parsedTorrent)
@@ -59,7 +61,7 @@ test('client.stop()', function (t) {
   }, 1000)
 })
 
-test('client.update()', function (t) {
+test('torrent: client.update()', function (t) {
   t.plan(3)
 
   var client = new Client(peerId, port, parsedTorrent, { interval: 5000 })
@@ -83,7 +85,7 @@ test('client.update()', function (t) {
   })
 })
 
-test('client.scrape()', function (t) {
+test('torrent: client.scrape()', function (t) {
   t.plan(4)
 
   var client = new Client(peerId, port, parsedTorrent)
@@ -101,5 +103,3 @@ test('client.scrape()', function (t) {
 
   client.scrape()
 })
-
-// TODO: add test where tracker doesn't support compact
diff --git a/test/udp-client.js b/test/udp-client.js
index 15a159c..e6e6de8 100644
--- a/test/udp-client.js
+++ b/test/udp-client.js
@@ -43,7 +43,7 @@ test('udp: client.start/update/stop()', function (t) {
         t.equal(typeof data.complete, 'number')
         t.equal(typeof data.incomplete, 'number')
       })
-      
+
       client.stop()
     })