diff --git a/dist/crc16.js b/dist/crc16.js
new file mode 100644
index 0000000..017627d
--- /dev/null
+++ b/dist/crc16.js
@@ -0,0 +1,66 @@
+/* @license
+ *
+ * CRC-CCITT (0xFFFF) library.
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2016
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+ // https://github.com/umdjs/umd
+(function(global, factory) {
+
+    if (typeof exports === 'object') {
+        // CommonJS (Node)
+        module.exports = factory();
+    } else if (typeof define === 'function' && define.amd) {
+        // AMD
+        define(factory);
+    } else {
+        // Browser global (with support for web workers)
+        global.crc16 = factory();
+    }
+
+}(this, function() {
+    'use strict';
+
+    /**
+     * Copied from Nordic's command line tool nrf.exe.
+     * https://github.com/NordicSemiconductor/pc-nrfutil/blob/master/nordicsemi/dfu/crc16.py
+     * CRC-CCITT (0xFFFF).
+     */
+    return function (binaryData) {
+        var crc = 0xFFFF;
+        var view = new Uint8Array(binaryData);
+        
+        var i;
+        
+        for (i = 0; i < view.byteLength; i++) {
+            crc = (crc >> 8 & 0x00FF) | (crc << 8 & 0xFF00);
+            crc ^= view[i];
+            crc ^= (crc & 0x00FF) >> 4;
+            crc ^= (crc << 8) << 4;
+            crc ^= ((crc & 0x00FF) << 4) << 1;
+        }
+        
+        return (crc & 0xFFFF);
+    };
+}));
diff --git a/dist/dfu.js b/dist/dfu.js
index 47a706d..a490392 100644
--- a/dist/dfu.js
+++ b/dist/dfu.js
@@ -162,9 +162,10 @@
         return view;
     }
 
-    function provision(device, arrayBuffer, imageType) {
+    function provision(device, arrayBuffer, crc, imageType) {
         return new Promise(function(resolve, reject) {
             var versionChar = null;
+            initPacket.crc = crc || 0xFFFF; // Not used in mbed/ older bootloader revisions.
             imageType = imageType || ImageType.Application;
 
             connect(device)
diff --git a/example_node.js b/example_node.js
index 7bc7f72..8568252 100644
--- a/example_node.js
+++ b/example_node.js
@@ -1,5 +1,6 @@
 var dfu = require('./index').dfu;
 var hex2bin = require('./index').hex2bin;
+var crc16 = require('./index').crc16;
 var fs = require('fs');
 
 var log = console.log;
@@ -40,8 +41,9 @@ dfu.findDevice({ services: [0x180D] })
     var hex = file.toString();
     var buffer = hex2bin(hex);
     log("file length: " + buffer.byteLength);
+    var crc = crc16(buffer);
 
-    return dfu.provision(device, buffer);
+    return dfu.provision(device, buffer, crc);
 })
 .then(() => process.exit())
 .catch(error => {
diff --git a/example_web.html b/example_web.html
index 1020141..d5a82fd 100644
--- a/example_web.html
+++ b/example_web.html
@@ -27,6 +27,7 @@
 
     <script src="dist/dfu.js"></script>
     <script src="dist/hex2bin.js"></script>
+    <script src="dist/crc16.js"></script>
 
     <script>
         var resultsEl = document.getElementById("results");
@@ -68,8 +69,9 @@
                 .then(hex => {
                     var buffer = hex2bin(hex);
                     log("downloaded length: " + buffer.byteLength);
+                    var crc = crc16(buffer);
 
-                    return dfu.provision(device, buffer);
+                    return dfu.provision(device, buffer, crc); // dfu.ImageType.Application is the default value for the fourth parameter. Specify this if you want to upload a softdevice/bootloader.
                 })
                 .then(() => {
                     log('dfu complete');
diff --git a/index.js b/index.js
index dcd4750..a7c72f0 100644
--- a/index.js
+++ b/index.js
@@ -2,8 +2,10 @@ require('bleat');
 
 var dfu = require('./dist/dfu');
 var hex2bin = require('./dist/hex2bin');
+var crc16 = require('./dist/crc16');
 
 module.exports = {
     dfu: dfu,
-    hex2bin: hex2bin
+    hex2bin: hex2bin,
+    crc16: crc16
 };
\ No newline at end of file