diff --git a/build/lib/updatePatches.js b/build/lib/updatePatches.js
index 8cacee861784..1a9fd1ca52f3 100644
--- a/build/lib/updatePatches.js
+++ b/build/lib/updatePatches.js
@@ -6,21 +6,46 @@ const util = require('../lib/util')
 const updatePatches = (options) => {
   config.update(options)
 
-  const runOptions = { cwd: config.projects.chrome.dir }
   const patchDir = path.join(config.projects['brave-core'].dir, 'patches')
 
+  const runOptionsChrome = { cwd: config.projects.chrome.dir }
+  const runOptionsPatch = { cwd: patchDir }
+
+  const desiredReplacementSeparator = '-'
+  const patchExtension = '.patch'
+
   console.log('updatePatches writing files to: ' + patchDir)
 
   // grab Modified (and later Deleted) files but not Created (since we copy those)
   const modifiedDiffArgs = ['diff', '--diff-filter=M', '--name-only', '--ignore-space-at-eol']
-  let modifiedDiff = util.run('git', modifiedDiffArgs, runOptions)
-  let moddedFileList = modifiedDiff.stdout.toString()
+  const modifiedDiff = util.run('git', modifiedDiffArgs, runOptionsChrome)
+  const modifiedFileList = modifiedDiff.stdout.toString()
     .split('\n')
     .filter(s => s.length > 0 && !s.startsWith('chrome/app/theme') &&
             !s.endsWith('.xtb') && !s.endsWith('.grd') && !s.endsWith('.grdp') &&
             !s.includes('google_update_idl'))
 
-  let n = moddedFileList.length
+  // copy array
+  let substitutedFileList = modifiedFileList.slice()
+
+  // replacing forward slashes and adding the patch extension to get nice filenames
+  // since git on Windows doesn't use backslashes, this is sufficient
+  substitutedFileList = substitutedFileList.map(s => s.replace(/\//g, desiredReplacementSeparator) + patchExtension)
+
+  // grab every existing patch file in the dir (at this point, patchfiles for now-unmodified files live on)
+  const existingFileArgs = ['ls-files', '--exclude-standard']
+  let existingFileOutput = util.run('git', existingFileArgs, runOptionsPatch)
+  let existingFileList = existingFileOutput.stdout.toString().split('\n').filter(s => s.length > 0)
+
+  // Add files here we specifically want to keep around regardless
+  const exclusionList = []
+
+  // Subtract to find which patchfiles no longer have diffs, yet still exist
+  const minuhend = existingFileList
+  const subtrahend = substitutedFileList.concat(exclusionList)
+  const difference = minuhend.filter(x => !subtrahend.includes(x))
+
+  const cruftList = difference
 
   // When splitting one large diff into a per-file diff, there are a few ways
   // you can go about it. Because different files can have the same name
@@ -32,27 +57,33 @@ const updatePatches = (options) => {
   // appear, you can quickly patch this by changing the separator, even
   // to something longer
 
-  const desiredReplacementSeparator = '-'
-  const patchExtension = '.patch'
-
-  for (var i = 0; i < n; i++) {
-    const old = moddedFileList[i]
-    let revised = old
+  let n = modifiedFileList.length
 
-    //replacing forward slashes
-    //since git on Windows doesn't use backslashes, this is sufficient
-    revised = revised.replace(/\//g, desiredReplacementSeparator)
+  for (let i = 0; i < n; i++) {
+    const old = modifiedFileList[i]
+    const revised = substitutedFileList[i]
 
     const singleDiffArgs = ['diff', '--src-prefix=a/', '--dst-prefix=b/', '--full-index', old]
-    let singleDiff = util.run('git', singleDiffArgs, runOptions)
+    let singleDiff = util.run('git', singleDiffArgs, runOptionsChrome)
 
     const contents = singleDiff.stdout.toString()
-    const filename = revised + patchExtension
+    const filename = revised
 
     fs.writeFileSync(path.join(patchDir, filename), contents)
 
     console.log('updatePatches wrote ' + (1 + i) + '/' + n + ': ' + filename)
   }
+
+  // regular rm patchfiles whose target is no longer modified
+  let m = cruftList.length
+  for (let i = 0; i < m; i++) {
+    let filename = cruftList[i]
+    let fullpath = path.join(patchDir, filename)
+
+    fs.removeSync(fullpath)
+
+    console.log('updatePatches *REMOVED* ' + (1 + i) + '/' + m + ': ' + filename)
+  }
 }
 
 module.exports = updatePatches