diff --git a/lib/encode.js b/lib/encode.js
index 7df9d4a..50c8fe7 100644
--- a/lib/encode.js
+++ b/lib/encode.js
@@ -168,6 +168,20 @@ function _encode(bytes, defers, value) {
         return 1;
       }
 
+      // Uint64BE (https://github.com/kawanet/int64-buffer)
+      if (value._isUint64BE) {
+        value = value.toArray();
+        bytes.push(0xcf, ...value);
+        return 9;
+      }
+
+      // Int64BE (https://github.com/kawanet/int64-buffer)
+      if (value._isInt64BE) {
+        value = value.toArray();
+        bytes.push(0xd3, ...value);
+        return 9;
+      }
+
       if (Array.isArray(value)) {
         length = value.length;
 
diff --git a/package-lock.json b/package-lock.json
index f0906d0..2fc0042 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -606,9 +606,9 @@
       "dev": true
     },
     "int64-buffer": {
-      "version": "0.1.9",
-      "resolved": "https://registry.npmjs.org/int64-buffer/-/int64-buffer-0.1.9.tgz",
-      "integrity": "sha1-ngOdoEOyT3ixlrKD4EZT716ZD2E=",
+      "version": "0.99.1007",
+      "resolved": "https://registry.npmjs.org/int64-buffer/-/int64-buffer-0.99.1007.tgz",
+      "integrity": "sha512-XDBEu44oSTqlvCSiOZ/0FoUkpWu/vwjJLGSKDabNISPQNZ5wub1FodGHBljRsrR0IXRPq7SslshZYMuA55CgTQ==",
       "dev": true
     },
     "is-buffer": {
@@ -917,6 +917,12 @@
         "isarray": "^1.0.0"
       },
       "dependencies": {
+        "int64-buffer": {
+          "version": "0.1.10",
+          "resolved": "https://registry.npmjs.org/int64-buffer/-/int64-buffer-0.1.10.tgz",
+          "integrity": "sha1-J3siiofZWtd30HwTgyAiQGpHNCM=",
+          "dev": true
+        },
         "isarray": {
           "version": "1.0.0",
           "resolved": "https://registry.npmjs.org/isarray/-/isarray-1.0.0.tgz",
diff --git a/package.json b/package.json
index 1124bda..fc06cdf 100644
--- a/package.json
+++ b/package.json
@@ -23,6 +23,7 @@
     "benchmark": "^2.1.2",
     "benchtable": "^0.1.0",
     "chai": "^3.5.0",
+    "int64-buffer": "^0.99.1007",
     "istanbul": "^0.4.5",
     "jshint": "^2.9.5",
     "mocha": "^3.2.0",
diff --git a/test/test.js b/test/test.js
index 6759274..b872c84 100644
--- a/test/test.js
+++ b/test/test.js
@@ -2,6 +2,7 @@
 
 const notepack = require('../');
 const expect = require('chai').expect;
+const { Int64BE, Uint64BE } = require('int64-buffer');
 
 function array(length) {
   const arr = new Array(length);
@@ -153,6 +154,14 @@ describe('notepack', function () {
     check(Math.pow(2, 63) + 1024, 'cf8000000000000000');
   });
 
+  it('Uint64BE', function () {
+    checkEncode(new Uint64BE(4294967296), 'cf0000000100000000');
+    checkEncode(new Uint64BE(Math.pow(2, 53) - 1), 'cf001fffffffffffff');
+    // unsafe unsigned integer
+    checkEncode(new Uint64BE('18446744073709551615'), 'cfffffffffffffffff');
+    checkEncode(new Uint64BE('18446744073709551614'), 'cffffffffffffffffe');
+  });
+
   // NOTE: We'll always encode a positive number as a uint, but we should be
   // able to decode a positive int value
 
@@ -206,6 +215,21 @@ describe('notepack', function () {
     check(-Math.pow(2, 63) - 1024, 'd38000000000000000');
   });
 
+  it('Int64BE', function () {
+    checkEncode(new Int64BE(-2147483649), 'd3ffffffff7fffffff');
+    checkEncode(new Int64BE(-4294967297), 'd3fffffffeffffffff');
+    checkEncode(new Int64BE(-65437650001231), 'd3ffffc47c1c1de2b1');
+    checkEncode(new Int64BE(-1111111111111111), 'd3fffc0d7348ea8e39');
+    checkEncode(new Int64BE(-1532678092380345), 'd3fffa8e0992bfa747');
+    checkEncode(new Int64BE(-4503599627370496), 'd3fff0000000000000');
+    checkEncode(new Int64BE(-7840340234323423), 'd3ffe42540896a3a21');
+    // Minimum safe signed integer
+    checkEncode(new Int64BE(-Math.pow(2, 53) + 1), 'd3ffe0000000000001');
+    // unsafe signed integer
+    checkEncode(new Int64BE('-9223372036854775808'), 'd38000000000000000');
+    checkEncode(new Int64BE('-9223372036854775807'), 'd38000000000000001');
+  });
+
   it('fixext 1 / undefined', function () {
     check(undefined, 'd40000');
     checkDecode([127, Buffer.from('a')], 'd4' + '7f' + '61');