diff --git a/app/assets/javascripts/repo/lib/diff/controller.js b/app/assets/javascripts/repo/lib/diff/controller.js
index 39c6cb92e0f..6c97f1cc24d 100644
--- a/app/assets/javascripts/repo/lib/diff/controller.js
+++ b/app/assets/javascripts/repo/lib/diff/controller.js
@@ -1,24 +1,25 @@
 /* global monaco */
-import Disposable from '../common/disposable';
 import DirtyDiffWorker from './worker';
+import Disposable from '../common/disposable';
 import decorationsController from '../decorations/controller';
 
 export const getDiffChangeType = (change) => {
-  if (change.originalEndLineNumber === 0) {
+  if (change.modified) {
+    return 'modified';
+  } else if (change.added) {
     return 'added';
-  } else if (change.modifiedEndLineNumber === 0) {
+  } else if (change.removed) {
     return 'removed';
   }
 
-  return 'modified';
+  return '';
 };
 
 export const getDecorator = change => ({
   range: new monaco.Range(
-    change.modifiedStartLineNumber,
+    change.lineNumber,
     1,
-    !change.modifiedEndLineNumber ?
-      change.modifiedStartLineNumber : change.modifiedEndLineNumber,
+    change.endLineNumber,
     1,
   ),
   options: {
@@ -37,22 +38,15 @@ export default class DirtyDiffController {
     this.disposable = new Disposable();
     this.editorSimpleWorker = null;
     this.modelManager = modelManager;
-    this.disposable.add(this.worker = new DirtyDiffWorker());
+    this.dirtyDiffWorker = new DirtyDiffWorker();
   }
 
   attachModel(model) {
-    if (model.attachedToWorker) return;
-
-    [model.getModel(), model.getOriginalModel()].forEach(() => {
-      this.worker.attachModel(model);
-    });
-
-    model.onChange((_, e) => this.computeDiff(model, e));
+    model.onChange(() => this.computeDiff(model));
   }
 
-  computeDiff(model, e) {
-    this.worker.modelChanged(model, e);
-    this.worker.compute(model, changes => decorate(model, changes));
+  computeDiff(model) {
+    decorate(model, this.dirtyDiffWorker.compute(model));
   }
 
   // eslint-disable-next-line class-methods-use-this
diff --git a/app/assets/javascripts/repo/lib/diff/worker.js b/app/assets/javascripts/repo/lib/diff/worker.js
index 39047d85507..0007c7060dc 100644
--- a/app/assets/javascripts/repo/lib/diff/worker.js
+++ b/app/assets/javascripts/repo/lib/diff/worker.js
@@ -1,77 +1,34 @@
-/* global monaco */
-import Disposable from '../common/disposable';
+import { diffLines } from 'diff';
 
 export default class DirtyDiffWorker {
-  constructor() {
-    this.editorSimpleWorker = null;
-    this.disposable = new Disposable();
-    this.actions = new Set();
+  // eslint-disable-next-line class-methods-use-this
+  compute(model) {
+    const originalContent = model.getOriginalModel().getValue();
+    const newContent = model.getModel().getValue();
+    const changes = diffLines(originalContent, newContent);
 
-    // eslint-disable-next-line promise/catch-or-return
-    monaco.editor.createWebWorker({
-      moduleId: 'vs/editor/common/services/editorSimpleWorker',
-    }).getProxy().then((editorSimpleWorker) => {
-      this.disposable.add(this.editorSimpleWorker = editorSimpleWorker);
-      this.ready();
-    });
-  }
+    let lineNumber = 1;
+    return changes.reduce((acc, change) => {
+      const findOnLine = acc.find(c => c.lineNumber === lineNumber);
 
-  // loop through all the previous cached actions
-  // this way we don't block the user from editing the file
-  ready() {
-    this.actions.forEach((action) => {
-      const methodName = Object.keys(action)[0];
-      this[methodName](...action[methodName]);
-    });
+      if (findOnLine) {
+        Object.assign(findOnLine, change, {
+          modified: true,
+          endLineNumber: change.count > 1 ? lineNumber + change.count : lineNumber,
+        });
+      } else if ('added' in change || 'removed' in change) {
+        acc.push(Object.assign({}, change, {
+          lineNumber,
+          modified: undefined,
+          endLineNumber: change.count > 1 ? lineNumber + change.count : lineNumber,
+        }));
+      }
 
-    this.actions.clear();
-  }
+      if (!change.removed) {
+        lineNumber += change.count;
+      }
 
-  attachModel(model) {
-    if (this.editorSimpleWorker && !model.attachedToWorker) {
-      this.editorSimpleWorker.acceptNewModel(model.diffModel);
-      this.editorSimpleWorker.acceptNewModel(model.originalDiffModel);
-
-      model.setAttachedToWorker(true);
-    } else if (!this.editorSimpleWorker) {
-      this.actions.add({
-        attachModel: [model],
-      });
-    }
-  }
-
-  modelChanged(model, e) {
-    if (this.editorSimpleWorker) {
-      this.editorSimpleWorker.acceptModelChanged(
-        model.url,
-        e,
-      );
-    } else {
-      this.actions.add({
-        modelChanged: [model, e],
-      });
-    }
-  }
-
-  compute(model, cb) {
-    if (this.editorSimpleWorker) {
-      return this.editorSimpleWorker.computeDiff(
-        model.originalUrl,
-        model.url,
-      ).then(cb);
-    }
-
-    this.actions.add({
-      compute: [model, cb],
-    });
-
-    return null;
-  }
-
-  dispose() {
-    this.actions.clear();
-
-    this.disposable.dispose();
-    this.editorSimpleWorker = null;
+      return acc;
+    }, []);
   }
 }
diff --git a/app/assets/javascripts/repo/lib/editor.js b/app/assets/javascripts/repo/lib/editor.js
index 173eacbd65c..ea3bfe16462 100644
--- a/app/assets/javascripts/repo/lib/editor.js
+++ b/app/assets/javascripts/repo/lib/editor.js
@@ -11,28 +11,27 @@ export default class Editor {
   }
 
   constructor() {
-    this.diffComputers = new Map();
     this.currentModel = null;
     this.instance = null;
     this.dirtyDiffController = null;
-    this.modelManager = new ModelManager();
     this.disposable = new Disposable();
 
-    this.disposable.add(this.modelManager);
+    this.disposable.add(
+      this.modelManager = new ModelManager(),
+    );
   }
 
   createInstance(domElement) {
     if (!this.instance) {
-      this.instance = monaco.editor.create(domElement, {
-        model: null,
-        readOnly: false,
-        contextmenu: true,
-        scrollBeyondLastLine: false,
-      });
-
-      this.dirtyDiffController = new DirtyDiffController(this.modelManager);
-
-      this.disposable.add(this.dirtyDiffController, this.instance);
+      this.disposable.add(
+        this.instance = monaco.editor.create(domElement, {
+          model: null,
+          readOnly: false,
+          contextmenu: true,
+          scrollBeyondLastLine: false,
+        }),
+        this.dirtyDiffController = new DirtyDiffController(this.modelManager),
+      );
     }
   }
 
diff --git a/package.json b/package.json
index 8c1b2c401ed..5b4676bf4ae 100644
--- a/package.json
+++ b/package.json
@@ -33,6 +33,7 @@
     "css-loader": "^0.28.0",
     "d3": "^3.5.11",
     "deckar01-task_list": "^2.0.0",
+    "diff": "^3.4.0",
     "document-register-element": "1.3.0",
     "dropzone": "^4.2.0",
     "emoji-unicode-version": "^0.2.1",
diff --git a/yarn.lock b/yarn.lock
index 73cc4f11500..2050f9eeed7 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -1895,6 +1895,10 @@ di@^0.0.1:
   version "0.0.1"
   resolved "https://registry.yarnpkg.com/di/-/di-0.0.1.tgz#806649326ceaa7caa3306d75d985ea2748ba913c"
 
+diff@^3.4.0:
+  version "3.4.0"
+  resolved "https://registry.yarnpkg.com/diff/-/diff-3.4.0.tgz#b1d85507daf3964828de54b37d0d73ba67dda56c"
+
 diffie-hellman@^5.0.0:
   version "5.0.2"
   resolved "https://registry.yarnpkg.com/diffie-hellman/-/diffie-hellman-5.0.2.tgz#b5835739270cfe26acf632099fded2a07f209e5e"