diff --git a/lib/http/base.js b/lib/http/base.js
index 127e1512..d7cb80de 100644
--- a/lib/http/base.js
+++ b/lib/http/base.js
@@ -213,7 +213,7 @@ HTTPBase.prototype._initIO = function _initIO() {
 
 HTTPBase.prototype._open = function open() {
   assert(typeof this.options.port === 'number', 'Port required.');
-  this.listen(this.options.port, this.options.host);
+  return this.listen(this.options.port, this.options.host);
 };
 
 /**
diff --git a/lib/http/rpc.js b/lib/http/rpc.js
index fb21702d..5b0628ce 100644
--- a/lib/http/rpc.js
+++ b/lib/http/rpc.js
@@ -3934,17 +3934,17 @@ RPC.prototype.signmessage = co(function* signmessage(args) {
   return sig.toString('base64');
 });
 
-RPC.prototype.walletlock = function walletlock(args) {
+RPC.prototype.walletlock = co(function* walletlock(args) {
   if (args.help || (this.wallet.master.encrypted && args.length !== 0))
     throw new RPCError('walletlock');
 
   if (!this.wallet.master.encrypted)
     throw new RPCError('Wallet is not encrypted.');
 
-  this.wallet.lock();
+  yield this.wallet.lock();
 
   return null;
-};
+});
 
 RPC.prototype.walletpassphrasechange = co(function* walletpassphrasechange(args) {
   var old, new_;
diff --git a/lib/http/server.js b/lib/http/server.js
index e7158adb..8c43323c 100644
--- a/lib/http/server.js
+++ b/lib/http/server.js
@@ -883,7 +883,7 @@ HTTPServer.prototype._initIO = function _initIO() {
         socket.join(id);
 
         callback();
-      }).catch(function(err) {
+      }, function(err) {
         self.logger.info('Wallet auth failure for %s: %s.', id, err.message);
         return callback({ error: 'Bad token.' });
       });
@@ -943,10 +943,13 @@ HTTPServer.prototype._initIO = function _initIO() {
     socket.on('scan chain', function(args, callback) {
       var start = args[0];
 
-      if (!utils.isHex256(start) && !utils.isNumber(start))
+      if (!utils.isHex256(start) && !utils.isUInt32(start))
         return callback({ error: 'Invalid parameter.' });
 
-      socket.scan(start).then(callback).catch(function(err) {
+      if (typeof start === 'string')
+        start = utils.revHex(start);
+
+      socket.scan(start).then(callback, function(err) {
         callback({ error: err.message });
       });
     });
@@ -1062,8 +1065,8 @@ HTTPServer.prototype.del = function del(path, callback) {
  * @see HTTPBase#listen
  */
 
-HTTPServer.prototype.listen = function listen(port, host, callback) {
-  this.server.listen(port, host, callback);
+HTTPServer.prototype.listen = function listen(port, host) {
+  return this.server.listen(port, host);
 };
 
 /**
@@ -1257,27 +1260,40 @@ ClientSocket.prototype.testFilter = function testFilter(tx) {
   }
 };
 
-ClientSocket.prototype.scan = function scan(start) {
-  var self = this;
-  var i;
+ClientSocket.prototype.scan = co(function* scan(start) {
+  var scanner = this.scanner.bind(this);
+  var entry;
 
-  if (typeof start === 'string')
-    start = utils.revHex(start);
+  if (this.chain.db.options.spv) {
+    entry = yield this.chain.db.get(start);
 
-  if (this.chain.db.options.spv)
-    return this.chain.reset(start);
+    if (!entry)
+      throw new Error('Block not found.');
+
+    if (!entry.isGenesis())
+      start = entry.prevBlock;
+
+    yield this.chain.reset(start);
+
+    return;
+  }
 
   if (this.chain.db.options.prune)
-    return Promise.reject(new Error('Cannot scan in pruned mode.'));
+    throw new Error('Cannot scan in pruned mode.');
 
-  return this.chain.db.scan(start, this.filter, co(function *(entry, txs) {
-    for (i = 0; i < txs.length; i++)
-      txs[i] = txs[i].toJSON();
+  yield this.chain.db.scan(start, this.filter, scanner);
+});
 
-    self.emit('block tx', entry.toJSON(), txs);
+ClientSocket.prototype.scanner = function scanner(entry, txs) {
+  var json = new Array(txs.length);
+  var i;
 
-    yield utils.wait();
-  }));
+  for (i = 0; i < txs.length; i++)
+    json[i] = txs[i].toJSON();
+
+  this.emit('block tx', entry.toJSON(), json);
+
+  return Promise.resolve(null);
 };
 
 ClientSocket.prototype.join = function join(id) {
diff --git a/lib/utils/spawn.js b/lib/utils/spawn.js
index 05e849f9..2f34305e 100644
--- a/lib/utils/spawn.js
+++ b/lib/utils/spawn.js
@@ -77,31 +77,6 @@ function co(generator) {
   };
 }
 
-/**
- * Wrap a generator function to be
- * executed into a function that
- * returns a promise (with a lock).
- * @param {String} name - lock name.
- * @param {GeneratorFunction}
- * @returns {Function}
- */
-
-function col(name, generator) {
-  var func = co(generator);
-  return co(function *() {
-    var unlock = yield this[name].lock();
-    var result;
-    try {
-      result = yield func.apply(this, arguments);
-    } catch (e) {
-      unlock();
-      throw e;
-    }
-    unlock();
-    return result;
-  });
-}
-
 /**
  * Wrap a generator function to be
  * executed into a function that
@@ -235,11 +210,11 @@ function wrap(resolve, reject) {
 
 function call(func) {
   var self = this;
-  var args = new Array(arguments.length);
+  var args = new Array(Math.max(0, arguments.length - 1));
   var i;
 
   for (i = 1; i < arguments.length; i++)
-    args[i] = arguments[i];
+    args[i - 1] = arguments[i];
 
   return new Promise(function(resolve, reject) {
     args.push(wrap(resolve, reject));
@@ -284,7 +259,6 @@ exports = spawn;
 exports.exec = exec;
 exports.spawn = spawn;
 exports.co = co;
-exports.col = col;
 exports.cob = cob;
 exports.con = con;
 exports.cb = cb;