diff --git a/src/vs/workbench/api/electron-browser/mainThreadComments.ts b/src/vs/workbench/api/electron-browser/mainThreadComments.ts
index fd3d2ef1e23..3a7b818a7c2 100644
--- a/src/vs/workbench/api/electron-browser/mainThreadComments.ts
+++ b/src/vs/workbench/api/electron-browser/mainThreadComments.ts
@@ -5,7 +5,7 @@
 'use strict';
 
 import { Disposable, IDisposable, dispose } from 'vs/base/common/lifecycle';
-import { ICodeEditor } from 'vs/editor/browser/editorBrowser';
+import { ICodeEditor, IDiffEditor } from 'vs/editor/browser/editorBrowser';
 import { ICodeEditorService } from 'vs/editor/browser/services/codeEditorService';
 import * as modes from 'vs/editor/common/modes';
 import { extHostNamedCustomer } from 'vs/workbench/api/electron-browser/extHostCustomers';
@@ -116,7 +116,17 @@ export class MainThreadComments extends Disposable implements MainThreadComments
 	getFocusedEditor(): ICodeEditor {
 		let editor = this._codeEditorService.getFocusedCodeEditor();
 		if (!editor) {
-			return this._editorService.activeTextEditorWidget as ICodeEditor;
+			/* please note that the type of `this._editorService.activeTextEditorWidget` is  `{ IEditor as ICodeEditor } from 'vs/editor/common/editorCommon'`
+			 * It's `IEditor` but renamed to `ICodeEditor`. The `ICodeEditor` in current context is `import { ICodeEditor } from 'vs/editor/browser/editorBrowser'`
+			 * this._editorService.activeTextEditorWidget is
+			 * 1. ICodeEditor extends editorCommon.IEditor
+			 * 2. IDiffEditor extends editorCommon.IEditor
+			 */
+			if ((this._editorService.activeTextEditorWidget as ICodeEditor).getContribution) {
+				return this._editorService.activeTextEditorWidget as ICodeEditor;
+			} else {
+				return (this._editorService.activeTextEditorWidget as IDiffEditor).getModifiedEditor();
+			}
 		}
 
 		return editor;