diff --git a/lib/sphinxapi.js b/lib/sphinxapi.js
index 862881f..27fec77 100644
--- a/lib/sphinxapi.js
+++ b/lib/sphinxapi.js
@@ -934,8 +934,109 @@ SphinxClient.prototype.BuildExcerpts = function (docs, index, words, opts, cb) {
 		return null;
 	});
 };
-SphinxClient.prototype.UpdateAttributes = function (index, attrs, values, mva) {
-	if (mva === undefined) mva = false;
+SphinxClient.prototype.UpdateAttributes = function (index, attrs, values, mva, fn) {
+/* === Validation === */
+
+    assert.equal(typeof index, 'string');
+    assert.equal(typeof attrs, 'object');
+    assert.equal(typeof values, 'object');
+    assert.equal(typeof mva, 'boolean');
+
+    for (var k in attrs) {
+        if (!attrs.hasOwnProperty(k)) continue;
+
+        assert.equal(typeof attrs[k], 'string');
+    }
+
+    for (var k in values) {
+        if (!values.hasOwnProperty(k)) continue;
+
+        // Document must be an array of attribute values.
+        assert.equal(typeof values[k], 'object');
+
+        // Number of attributes do not match.
+        assert.equal(len(values[k]), len(attrs));
+
+        for (var v in values[k]) {
+            if (!values[k].hasOwnProperty(v)) continue;
+
+            if (mva) {
+                // MVA must be an array.
+                assert.equal(typeof values[k][v], 'object');
+
+                for (var vv in values[k][v]) {
+                    if (!values[k][v].hasOwnProperty(vv)) continue;
+
+                    // Attribute value must be numeric.
+                    assert.equal(typeof values[k][v][vv], 'number');
+                }
+            } else {
+                // Attribute value must be numeric.
+                assert.equal(typeof values[k][v], 'number');
+            }
+        }
+    }
+
+/* === Build request === */
+
+    var req = [];
+
+    // index
+    req.push(pack('>L', [len(index)]), index);
+
+    // attrs
+    req.push(pack('>L', [len(attrs)]));
+    for (var k in attrs) {
+        if (!attrs.hasOwnProperty(k)) continue;
+
+        req.push(pack('>L', [len(attrs[k])]), attrs[k]);
+        req.push(pack('>L', [mva?1:0]));
+    }
+
+
+    // values
+    req.push(pack('>L', [len(values)]));
+    for (var k in values) {
+        if (!values.hasOwnProperty(k)) continue;
+
+        req.push(packUInt64(k));
+
+        for (var v in values[k]) {
+            if (!values[k].hasOwnProperty(v)) continue;
+
+            if (mva) {
+                req.push(pack('>L', [len(values[k][v])]));
+
+                for (var vv in values[k][v]) {
+                    if (!values[k][v].hasOwnProperty(vv)) continue;
+
+                    req.push(pack('>L', [values[k][v][vv]]));
+                }
+            } else {
+                req.push(pack('>L', [values[k][v]]));
+            }
+        }
+    }
+
+    var reqData = req.reduce(ReduceBuffer, new Buffer(''));
+    var length = reqData.length;
+
+/* Send request */
+
+    var self = this;
+    var request = ConcatBuffer(pack('>2HL', [SphinxClient.SEARCHD_COMMAND_UPDATE, SphinxClient.VER_COMMAND_UPDATE, length]), reqData);
+    this._SendRequest(SphinxClient.VER_COMMAND_UPDATE, request, function (err, response) {
+        if (err) {
+            return fn(err, null);
+        }
+        if (response.length != 4) {
+            self._error = 'unexpected response length';
+            return fn(err, null);
+        }
+
+        var amount = Number(unpack('>L', response.slice(0, 4)));
+        return fn(err, amount);
+    });
 };
 SphinxClient.prototype.BuildKeywords = function (query, index, hits, cb ) {
 	assert.equal(typeof query, 'string');