diff --git a/__tests__/spec/build.js b/__tests__/spec/build.js
index da74055ae2..b65abee332 100644
--- a/__tests__/spec/build.js
+++ b/__tests__/spec/build.js
@@ -85,6 +85,11 @@ describe('the build pipeline', () => {
     })
 
     it('copies javascript to the public folder', () => {
+      expect(fs.copyFileSync).toHaveBeenCalledWith(
+        path.join(projectDir, 'lib', 'assets', 'javascripts', 'kit.js'),
+        path.join('public', '_kit', 'javascripts', 'kit.js')
+      )
+
       expect(fs.copyFileSync).toHaveBeenCalledWith(
         path.join('app', 'assets', 'javascripts', 'application.js'),
         path.join('public', 'javascripts', 'application.js')
diff --git a/__tests__/spec/update-script.js b/__tests__/spec/update-script.js
index c173a52940..9a881d28e7 100644
--- a/__tests__/spec/update-script.js
+++ b/__tests__/spec/update-script.js
@@ -14,7 +14,7 @@ const execPromise = promisify(child_process.exec)
 const execFilePromise = promisify(child_process.execFile)
 
 // This is a long-running test
-jest.setTimeout(60000)
+jest.setTimeout(120000)
 
 function testSkipFailingIf (condition, ...args) {
   if (condition) {
@@ -511,6 +511,37 @@ describe('update.sh', () => {
     })
   })
 
+  describe('post', () => {
+    let testDir, gitStatus
+
+    beforeAll(async () => {
+      testDir = await mktestPrototype(
+        'update-post', { ref: 'v12.1.1' }
+      )
+
+      await runScriptAndExpectSuccess('post', { testDir })
+
+      gitStatus = await execGitStatus(testDir)
+    })
+
+    it('updates app stylesheets', () => {
+      expect(gitStatus).toEqual(expect.arrayContaining([
+        ' M app/assets/sass/application.scss',
+        ' D app/assets/sass/application-ie8.scss',
+        ' D app/assets/sass/unbranded-ie8.scss'
+      ]))
+    })
+
+    it('updates app javascripts', () => {
+      expect(gitStatus).toEqual(expect.arrayContaining([
+        ' M app/assets/javascripts/application.js',
+        ' D app/assets/javascripts/auto-store-data.js',
+        ' D app/assets/javascripts/jquery-1.11.3.js',
+        ' D app/assets/javascripts/step-by-step-nav.js'
+      ]))
+    })
+  })
+
   it('can be run as a piped script', async () => {
     const testDir = await mktestPrototype('pipe')
 
diff --git a/app/assets/javascripts/application.js b/app/assets/javascripts/application.js
index 5600fb7b84..277b4f5578 100644
--- a/app/assets/javascripts/application.js
+++ b/app/assets/javascripts/application.js
@@ -1,20 +1,3 @@
-window.GOVUKPrototypeKit = {
-  documentReady: function (fn) {
-    if (document.readyState !== 'loading') {
-      // IE9 support
-      fn()
-    } else {
-      // Everything else
-      document.addEventListener('DOMContentLoaded', fn)
-    }
-  }
-}
-
-// Warn about using the kit in production
-if (window.console && window.console.info) {
-  window.console.info('GOV.UK Prototype Kit - do not use for production')
-}
-
-window.GOVUKPrototypeKit.documentReady(function () {
-  window.GOVUKFrontend.initAll()
+window.GOVUKPrototypeKit.documentReady(() => {
+  // Add JavaScript here
 })
diff --git a/app/views/includes/scripts.html b/app/views/includes/scripts.html
index 40960cd667..b078c8efb8 100644
--- a/app/views/includes/scripts.html
+++ b/app/views/includes/scripts.html
@@ -3,8 +3,9 @@
   <script src="{{scriptUrl}}"></script>
 {% endfor %}
 
+<script src="/public/_kit/javascripts/kit.js"></script>
 <script src="/public/javascripts/application.js"></script>
 
 {% if useAutoStoreData %}
-  <script src="/public/javascripts/auto-store-data.js"></script>
+  <script src="/public/_kit/javascripts/auto-store-data.js"></script>
 {% endif %}
diff --git a/cypress/integration/1-watch-files/watch-javascripts.cypress.js b/cypress/integration/1-watch-files/watch-javascripts.cypress.js
index b9fa1293da..30b0406da1 100644
--- a/cypress/integration/1-watch-files/watch-javascripts.cypress.js
+++ b/cypress/integration/1-watch-files/watch-javascripts.cypress.js
@@ -22,7 +22,7 @@ describe('watch application.js', () => {
     const onAlert = cy.stub()
     cy.on('window:alert', onAlert)
 
-    const markerText = 'window.GOVUKFrontend.initAll()'
+    const markerText = '// Add JavaScript here'
     const newText = markerText + '\n  ' + "window.alert('Test')"
 
     cy.task('replaceTextInFile', {
diff --git a/lib/_update/post.js b/lib/_update/post.js
new file mode 100644
index 0000000000..521e06803f
--- /dev/null
+++ b/lib/_update/post.js
@@ -0,0 +1,5 @@
+const { updateJavascripts } = require('./update-javascripts')
+const { updateScss } = require('./update-scss')
+
+updateJavascripts()
+updateScss()
diff --git a/lib/_update/update-javascripts.js b/lib/_update/update-javascripts.js
new file mode 100644
index 0000000000..dc222304c9
--- /dev/null
+++ b/lib/_update/update-javascripts.js
@@ -0,0 +1,29 @@
+const fs = require('fs').promises
+const path = require('path')
+
+const { getProjectVersion, patchUserFile } = require('./util')
+const { projectDir } = require('../path-utils')
+
+async function updateJavascripts () {
+  // Delete any old shared files
+  const appJsPath = path.join(projectDir, 'app', 'assets', 'javascripts')
+  await fs.unlink(path.join(appJsPath, 'auto-store-data.js')).catch(() => {})
+  await fs.unlink(path.join(appJsPath, 'jquery-1.11.3.js')).catch(() => {})
+  await fs.unlink(path.join(appJsPath, 'step-by-step-nav.js')).catch(() => {})
+  await fs.unlink(path.join(appJsPath, 'step-by-step-navigation.js')).catch(() => {})
+
+  const userVersion = await getProjectVersion()
+
+  // If the user already has version 13 or greater of the kit installed then
+  // their application.js file is all their code and we don't don't want to
+  // change it
+  if (userVersion >= '13.0.0') {
+    return
+  }
+
+  await patchUserFile(userVersion, 'app/assets/javascripts/application.js')
+}
+
+module.exports = {
+  updateJavascripts
+}
diff --git a/lib/_update/update-javascripts.test.js b/lib/_update/update-javascripts.test.js
new file mode 100644
index 0000000000..3658d17699
--- /dev/null
+++ b/lib/_update/update-javascripts.test.js
@@ -0,0 +1,124 @@
+/* eslint-env jest */
+
+const fs = require('fs')
+const fsp = require('fs').promises
+const path = require('path')
+
+jest.mock('./util/fetch-original')
+jest.mock('./util', () => {
+  const originalModule = jest.requireActual('./util')
+
+  return {
+    ...originalModule,
+    getProjectVersion: jest.fn(async () => '')
+  }
+})
+const { fetchOriginal: mockFetchOriginal } = require('./util/fetch-original')
+const { getProjectVersion: mockGetProjectVersion } = require('./util')
+const { projectDir } = require('../path-utils')
+
+const { updateJavascripts } = require('./update-javascripts')
+
+const originalApplicationJs = `/* global $ */
+
+// Warn about using the kit in production
+if (window.console && window.console.info) {
+  window.console.info('GOV.UK Prototype Kit - do not use for production')
+}
+
+$(document).ready(function () {
+  window.GOVUKFrontend.initAll()
+})
+`
+const newApplicationJs = fs.readFileSync(
+  path.join('app', 'assets', 'javascripts', 'application.js'),
+  'utf8'
+)
+
+describe('updateJavascripts', () => {
+  let mockCopyFile, mockReadFile, mockUnlink, mockWriteFile
+
+  beforeEach(async () => {
+    mockGetProjectVersion.mockResolvedValue(
+      '12.1.1'
+    )
+
+    mockFetchOriginal.mockResolvedValue(
+      originalApplicationJs
+    )
+
+    mockReadFile = jest.spyOn(fsp, 'readFile').mockResolvedValue(
+      newApplicationJs
+    )
+
+    mockCopyFile = jest.spyOn(fsp, 'copyFile').mockImplementation(async () => {})
+    mockUnlink = jest.spyOn(fsp, 'unlink').mockImplementation(async () => {})
+    mockWriteFile = jest.spyOn(fsp, 'writeFile').mockImplementation(async () => {})
+  })
+
+  afterEach(() => {
+    jest.restoreAllMocks()
+  })
+
+  it('replaces application.js if the user has not updated it', async () => {
+    // theirs
+    mockReadFile.mockResolvedValueOnce(
+      originalApplicationJs
+    )
+
+    await updateJavascripts()
+
+    expect(mockCopyFile).toHaveBeenCalledWith(
+      path.join(projectDir, 'update', 'app', 'assets', 'javascripts', 'application.js'),
+      path.join(projectDir, 'app', 'assets', 'javascripts', 'application.js')
+    )
+  })
+
+  it('rewrites application.js if the user has added lines to the bottom of the file', async () => {
+    // theirs
+    mockReadFile.mockResolvedValueOnce(
+      originalApplicationJs + '\ncallMyCode()\n'
+    )
+    // ours
+    mockReadFile.mockResolvedValue(
+      newApplicationJs
+    )
+
+    await updateJavascripts()
+
+    expect(mockWriteFile).toHaveBeenCalledWith(
+      path.join(projectDir, 'app', 'assets', 'javascripts', 'application.js'),
+      newApplicationJs + '\ncallMyCode()\n',
+      'utf8'
+    )
+  })
+
+  it('does not touch application.js if the user prototype is already on v13', async () => {
+    mockGetProjectVersion.mockResolvedValue(
+      '13.0.0'
+    )
+
+    await updateJavascripts()
+
+    expect(mockReadFile).not.toHaveBeenCalled()
+    expect(mockWriteFile).not.toHaveBeenCalled()
+    expect(mockCopyFile).not.toHaveBeenCalled()
+  })
+
+  it('removes files that have been moved from app folder', async () => {
+    await updateJavascripts()
+
+    expect(mockUnlink).toHaveBeenCalledWith(
+      path.join(projectDir, 'app', 'assets', 'javascripts', 'auto-store-data.js')
+    )
+    expect(mockUnlink).toHaveBeenCalledWith(
+      path.join(projectDir, 'app', 'assets', 'javascripts', 'jquery-1.11.3.js')
+    )
+    expect(mockUnlink).toHaveBeenCalledWith(
+      path.join(projectDir, 'app', 'assets', 'javascripts', 'step-by-step-nav.js')
+    )
+    expect(mockUnlink).toHaveBeenCalledWith(
+      path.join(projectDir, 'app', 'assets', 'javascripts', 'step-by-step-navigation.js')
+    )
+  })
+})
diff --git a/lib/_update/update-scss/index.js b/lib/_update/update-scss/index.js
new file mode 100644
index 0000000000..59e7579d66
--- /dev/null
+++ b/lib/_update/update-scss/index.js
@@ -0,0 +1,16 @@
+const {
+  appSassPatternsPath,
+  libSassPatternsPath,
+  appSassPath,
+  libSassPath,
+  removeKitSassFromApplicationSass,
+  removeKitSassFromAppSassPath,
+  removeLegacyIE8Sass
+} = require('./update_scss')
+
+module.exports.updateScss = function () {
+  removeKitSassFromApplicationSass()
+  removeKitSassFromAppSassPath(appSassPatternsPath, libSassPatternsPath)
+  removeKitSassFromAppSassPath(appSassPath, libSassPath)
+  removeLegacyIE8Sass()
+}
diff --git a/lib/_update_scss/update_scss.js b/lib/_update/update-scss/update_scss.js
similarity index 97%
rename from lib/_update_scss/update_scss.js
rename to lib/_update/update-scss/update_scss.js
index 16d1c3fcbe..e179518b3a 100644
--- a/lib/_update_scss/update_scss.js
+++ b/lib/_update/update-scss/update_scss.js
@@ -1,6 +1,6 @@
 const path = require('path')
 const fs = require('fs')
-const { projectDir, packageDir } = require('../path-utils')
+const { projectDir, packageDir } = require('../../path-utils')
 const appSassPath = path.join(projectDir, 'app', 'assets', 'sass')
 const appSassPatternsPath = path.join(appSassPath, 'patterns')
 const applicationScssPath = path.join(appSassPath, 'application.scss')
diff --git a/lib/_update_scss/update_scss.test.js b/lib/_update/update-scss/update_scss.test.js
similarity index 97%
rename from lib/_update_scss/update_scss.test.js
rename to lib/_update/update-scss/update_scss.test.js
index 12f67f4c62..eec65daa42 100644
--- a/lib/_update_scss/update_scss.test.js
+++ b/lib/_update/update-scss/update_scss.test.js
@@ -4,7 +4,7 @@ const fs = require('fs')
 const path = require('path')
 const updateKit = require('./update_scss')
 const { appSassPath } = require('./update_scss')
-const { projectDir } = require('../path-utils')
+const { projectDir } = require('../../path-utils')
 
 describe('scripts/update-kit', () => {
   afterEach(() => {
diff --git a/lib/_update/util/fetch-original.js b/lib/_update/util/fetch-original.js
new file mode 100644
index 0000000000..81a5ea1115
--- /dev/null
+++ b/lib/_update/util/fetch-original.js
@@ -0,0 +1,33 @@
+const https = require('https')
+
+async function fetchOriginal (version, filePath) {
+  const remoteUrl = `https://raw.githubusercontent.com/alphagov/govuk-prototype-kit/v${version}/${filePath}`
+
+  let data = ''
+  return new Promise((resolve, reject) => {
+    https.get(remoteUrl, (response) => {
+      let error
+
+      if (response.statusCode !== 200) {
+        error = new Error(`could not fetch ${remoteUrl}: status code ${response.statusCode}`)
+        Object.assign(error, response)
+        response.resume()
+        reject(error)
+      }
+
+      response.setEncoding('utf8')
+
+      response.on('data', (chunk) => {
+        data += chunk
+      })
+
+      response.on('end', () => {
+        resolve(data)
+      })
+    })
+  })
+}
+
+module.exports = {
+  fetchOriginal
+}
diff --git a/lib/_update/util/fetch-original.test.js b/lib/_update/util/fetch-original.test.js
new file mode 100644
index 0000000000..1f4fe76011
--- /dev/null
+++ b/lib/_update/util/fetch-original.test.js
@@ -0,0 +1,29 @@
+/* eslint-env jest */
+
+const https = require('https')
+const stream = require('stream')
+
+const { fetchOriginal } = require('./fetch-original')
+
+describe('fetchOriginal', () => {
+  it('gets the contents of a file as of version from GitHub', async () => {
+    const mockHttpsGet = jest.spyOn(https, 'get').mockImplementation((url, callback) => {
+      const response = new stream.PassThrough()
+      response.statusCode = 200
+
+      callback(response)
+
+      response.write('foo\n')
+      response.write('bar\n')
+      response.end()
+    })
+
+    await expect(fetchOriginal('99.99.99', 'app/views/foo.html')).resolves.toEqual(
+      'foo\nbar\n'
+    )
+    expect(mockHttpsGet).toHaveBeenCalledWith(
+      'https://raw.githubusercontent.com/alphagov/govuk-prototype-kit/v99.99.99/app/views/foo.html',
+      expect.anything()
+    )
+  })
+})
diff --git a/lib/_update/util/index.js b/lib/_update/util/index.js
new file mode 100644
index 0000000000..b6493bb784
--- /dev/null
+++ b/lib/_update/util/index.js
@@ -0,0 +1,61 @@
+const fs = require('fs').promises
+const path = require('path')
+
+const { projectDir } = require('../../path-utils')
+const { fetchOriginal } = require('./fetch-original')
+
+const updateDir = path.join(projectDir, 'update')
+
+async function getProjectVersion () {
+  return (await fs.readFile(path.join(projectDir, 'VERSION.txt'), 'utf8')).trim()
+}
+
+async function patchUserFile (originalVersion, filePath) {
+  const theirs = await fs.readFile(path.resolve(projectDir, filePath), 'utf8')
+  let original = await fetchOriginal(originalVersion, filePath)
+  let ours = await fs.readFile(path.resolve(updateDir, filePath), 'utf8')
+
+  // Normalise line endings to match their file
+  var eol = '\n'
+  if (theirs.includes('\r\n')) {
+    eol = '\r\n'
+    if (!original.includes(eol)) {
+      original = original.replace(/\n/g, eol)
+    }
+    if (!ours.includes(eol)) {
+      ours = ours.replace(/\n/g, eol)
+    }
+  }
+
+  // It is possible that the file has already been upgraded, in which case there is nothing to do
+  if (theirs === ours) {
+    return
+  }
+
+  // If the user hasn't changed the file we can just replace it completely
+  if (original === theirs) {
+    return fs.copyFile(path.join(updateDir, filePath), path.join(projectDir, filePath))
+  }
+
+  // Otherwise, if the original code is contained as-is in their file, we can
+  // remove the shared lines, and add our hints
+  if (theirs.includes(original)) {
+    let merged
+    merged = theirs.replace(original, '')
+    merged = ours + merged
+    return fs.writeFile(path.resolve(projectDir, filePath), merged, 'utf8')
+  }
+
+  // If the original code is not recognisable, we should give up, but not
+  // without giving a warning to the user
+  console.warn(
+    `WARNING: update.sh was not able to automatically update your ${filePath} file.\n` +
+    'If you have a problem when running your prototype contact the GOV.UK Prototype team for support,\n' +
+    'using one of the methods listed at https://design-system.service.gov.uk/get-in-touch/'
+  )
+}
+
+module.exports = {
+  getProjectVersion,
+  patchUserFile
+}
diff --git a/lib/_update/util/index.test.js b/lib/_update/util/index.test.js
new file mode 100644
index 0000000000..a51924642a
--- /dev/null
+++ b/lib/_update/util/index.test.js
@@ -0,0 +1,144 @@
+/* eslint-env jest */
+
+const fs = require('fs').promises
+const path = require('path')
+
+jest.mock('./fetch-original')
+const { fetchOriginal: mockFetchOriginal } = require('./fetch-original')
+const { projectDir } = require('../../path-utils')
+
+const { getProjectVersion, patchUserFile } = require('./index.js')
+
+afterEach(() => {
+  jest.restoreAllMocks()
+})
+
+describe('getProjectVersion', () => {
+  it('reads the VERSION.txt file to get the version number', async () => {
+    const mockReadFile = jest.spyOn(fs, 'readFile').mockImplementation(
+      async () => '99.99.99\n'
+    )
+
+    await expect(getProjectVersion()).resolves.toEqual('99.99.99')
+    expect(mockReadFile).toHaveBeenCalledWith(
+      expect.stringContaining(`${path.sep}VERSION.txt`),
+      'utf8'
+    )
+  })
+})
+
+describe('patchUserFile', () => {
+  const filePath = 'app/assets/javascripts/application.js'
+
+  const originalContents = `/* global $ */
+$(document).ready(function () {
+  window.GOVUKFrontend.initAll()
+})
+`
+
+  const newContents = `window.GOVUKPrototypeKit.ready(() => {
+  // Add JavaScript here
+})
+`
+
+  let mockCopyFile, mockReadFile, mockWriteFile
+
+  beforeEach(() => {
+    mockFetchOriginal.mockResolvedValue(
+      originalContents
+    )
+
+    mockReadFile = jest.spyOn(fs, 'readFile').mockResolvedValue(
+      newContents
+    )
+
+    mockCopyFile = jest.spyOn(fs, 'copyFile').mockImplementation(() => {})
+    mockWriteFile = jest.spyOn(fs, 'writeFile').mockImplementation(() => {})
+  })
+
+  it('gets the original contents to compare with the user file', async () => {
+    mockReadFile.mockResolvedValue(
+      originalContents
+    )
+
+    mockFetchOriginal.mockResolvedValue(
+      originalContents
+    )
+
+    await patchUserFile('99.99.99', filePath)
+
+    expect(mockFetchOriginal).toHaveBeenCalledWith(
+      '99.99.99', filePath
+    )
+  })
+
+  it('replaces file if the user has not updated it', async () => {
+    mockReadFile.mockResolvedValueOnce(
+      originalContents
+    )
+
+    await patchUserFile('99.99.99', filePath)
+
+    expect(mockCopyFile).toHaveBeenCalledWith(
+      path.join(projectDir, 'update', 'app', 'assets', 'javascripts', 'application.js'),
+      path.join(projectDir, 'app', 'assets', 'javascripts', 'application.js')
+    )
+  })
+
+  it('rewrites file if the user has added lines to the bottom of the file', async () => {
+    // theirs
+    jest.spyOn(fs, 'readFile').mockResolvedValueOnce(
+      originalContents + '\ncallMyCode()\n'
+    )
+    // ours
+    jest.spyOn(fs, 'readFile').mockResolvedValueOnce(
+      newContents
+    )
+
+    await patchUserFile('99.99.99', filePath)
+
+    expect(mockWriteFile).toHaveBeenCalledWith(
+      expect.stringContaining(path.join('app', 'assets', 'javascripts', 'application.js')),
+      newContents + '\ncallMyCode()\n',
+      'utf8'
+    )
+  })
+
+  it('warns user and does not touch file if the user has rewritten it a lot', async () => {
+    // theirs
+    jest.spyOn(fs, 'readFile').mockImplementationOnce(
+      async () => 'justMyCode()\n'
+    )
+    // ours
+    jest.spyOn(fs, 'readFile').mockResolvedValueOnce(
+      newContents
+    )
+
+    const mockConsoleWarn = jest.spyOn(global.console, 'warn').mockImplementation(() => {})
+
+    await patchUserFile('99.99.99', filePath)
+
+    expect(mockWriteFile).not.toHaveBeenCalled()
+    expect(mockCopyFile).not.toHaveBeenCalled()
+    expect(mockConsoleWarn).toHaveBeenCalled()
+  })
+
+  it('does nothing if file has already been updated somehow', async () => {
+    // theirs
+    jest.spyOn(fs, 'readFile').mockResolvedValueOnce(
+      newContents
+    )
+    // ours
+    jest.spyOn(fs, 'readFile').mockResolvedValueOnce(
+      newContents
+    )
+
+    const mockConsoleWarn = jest.spyOn(global.console, 'warn')
+
+    await patchUserFile('99.99.99', filePath)
+
+    expect(mockWriteFile).not.toHaveBeenCalled()
+    expect(mockCopyFile).not.toHaveBeenCalled()
+    expect(mockConsoleWarn).not.toHaveBeenCalled()
+  })
+})
diff --git a/lib/_update_scss/index.js b/lib/_update_scss/index.js
deleted file mode 100644
index 460f625727..0000000000
--- a/lib/_update_scss/index.js
+++ /dev/null
@@ -1,14 +0,0 @@
-const {
-  appSassPatternsPath,
-  libSassPatternsPath,
-  appSassPath,
-  libSassPath,
-  removeKitSassFromApplicationSass,
-  removeKitSassFromAppSassPath,
-  removeLegacyIE8Sass
-} = require('./update_scss')
-
-removeKitSassFromApplicationSass()
-removeKitSassFromAppSassPath(appSassPatternsPath, libSassPatternsPath)
-removeKitSassFromAppSassPath(appSassPath, libSassPath)
-removeLegacyIE8Sass()
diff --git a/app/assets/javascripts/auto-store-data.js b/lib/assets/javascripts/auto-store-data.js
similarity index 100%
rename from app/assets/javascripts/auto-store-data.js
rename to lib/assets/javascripts/auto-store-data.js
diff --git a/lib/assets/javascripts/kit.js b/lib/assets/javascripts/kit.js
new file mode 100644
index 0000000000..5600fb7b84
--- /dev/null
+++ b/lib/assets/javascripts/kit.js
@@ -0,0 +1,20 @@
+window.GOVUKPrototypeKit = {
+  documentReady: function (fn) {
+    if (document.readyState !== 'loading') {
+      // IE9 support
+      fn()
+    } else {
+      // Everything else
+      document.addEventListener('DOMContentLoaded', fn)
+    }
+  }
+}
+
+// Warn about using the kit in production
+if (window.console && window.console.info) {
+  window.console.info('GOV.UK Prototype Kit - do not use for production')
+}
+
+window.GOVUKPrototypeKit.documentReady(function () {
+  window.GOVUKFrontend.initAll()
+})
diff --git a/lib/build/tasks.js b/lib/build/tasks.js
index 410aaff022..b8d60f99ae 100644
--- a/lib/build/tasks.js
+++ b/lib/build/tasks.js
@@ -16,7 +16,8 @@ const { projectDir, packageDir } = require('../path-utils')
 const { paths } = buildConfig
 
 const appSassPath = path.join(projectDir, paths.assets, 'sass')
-const libSassPath = path.join(packageDir, paths.libAssets, 'sass')
+const libAssetsPath = path.join(packageDir, paths.libAssets)
+const libSassPath = path.join(libAssetsPath, 'sass')
 const tempPath = path.join(projectDir, '.tmp')
 const tempSassPath = path.join(tempPath, 'sass')
 
@@ -46,6 +47,7 @@ function generateAssetsSync ({ verbose } = {}) {
   if (verbose) process.stdout.write('done\n')
 
   if (verbose) process.stdout.write('copying assets...')
+  copyAssets(libAssetsPath, path.join(paths.public, '_kit'))
   copyAssets(paths.assets, paths.public)
   if (verbose) process.stdout.write('done\n')
 }
diff --git a/update.sh b/update.sh
index 2af30c4725..ee94decbfd 100755
--- a/update.sh
+++ b/update.sh
@@ -170,6 +170,16 @@ copy () {
 
 	trap - ERR
 
+	update_gitignore
+}
+
+post () {
+	if [ -f 'update/lib/_update/post.js' ]; then
+		node 'update/lib/_update/post'
+	fi
+}
+
+finish () {
 	msg
 	msg "Your prototype kit files have now been updated, from version ${OLD_VERSION} to ${NEW_VERSION}."
 	msg 'If you need to make configuration changes, follow the steps at'
@@ -180,13 +190,6 @@ copy () {
 	update_gitignore
 }
 
-post () {
-  # execute _update_scss if it exists in the update folder
-  if [ -d "update/lib/_update_scss" ]; then
-    node "update/lib/_update_scss"
-  fi
-}
-
 if [ "$0" == "${BASH_SOURCE:-$0}" ]
 then
 	check
@@ -195,4 +198,5 @@ then
 	extract
 	copy
 	post
+	finish
 fi