diff --git a/src/vs/vscode.d.ts b/src/vs/vscode.d.ts
index 4cca5c91cf0bb9564435f6e8bb5510a6b5636d87..00e8ef06a0b5a94751e3e7c67dafb9d159d4c3b6 100644
--- a/src/vs/vscode.d.ts
+++ b/src/vs/vscode.d.ts
@@ -3557,6 +3557,52 @@ declare namespace vscode {
 		contentChanges: TextDocumentContentChangeEvent[];
 	}
 
+	/**
+	 * An event that is fired when a [document](#TextDocument) will be saved.
+	 *
+	 * To make modifications to the document before it is being saved, call the
+	 * [`waitUntil`](#TextDocumentWillSaveEvent.waitUntil)-function with a thenable
+	 * that resolves to an array of [text edits](#TextEdit).
+	 */
+	export interface TextDocumentWillSaveEvent {
+
+		/**
+		 * The document that will be saved.
+		 */
+		document: vscode.TextDocument;
+
+		/**
+		 * Allows to pause the event loop and to apply [pre-save-edits](#TextEdit).
+		 * Edits of subsequent calls to this function will be applied in order. The
+		 * edits will be *ignored* if concurrent modifications of the document happened.
+		 *
+		 * *Note:* This function can only be called during event dispatch and not
+		 * in an asynchronous manner:
+		 *
+		 * ```ts
+		 * workspace.onWillSaveTextDocument(event => {
+			// async, will *throw* an error
+		 	setTimeout(() => event.waitUntil(promise));
+
+		 	// sync, OK
+		 *	event.waitUntil(promise);
+		 * })
+		 * ```
+		 *
+		 * @param thenable A thenable that resolves to [pre-save-edits](#TextEdit).
+		 */
+		waitUntil(thenable: Thenable<vscode.TextEdit[]>): void;
+
+		/**
+		 * Allows to pause the event loop until the provided thenable resolved.
+		 *
+		 * *Note:* This function can only be called during event dispatch.
+		 *
+		 * @param thenable A thenable that delays saving.
+		 */
+		waitUntil(thenable: Thenable<any>): void;
+	}
+
 	/**
 	 * Namespace for dealing with the current workspace. A workspace is the representation
 	 * of the folder that has been opened. There is no workspace when just a file but not a
@@ -3692,6 +3738,11 @@ declare namespace vscode {
 		 */
 		export const onDidChangeTextDocument: Event<TextDocumentChangeEvent>;
 
+		/**
+		 * An event that is emitted when a [text document](#TextDocument) will be saved to disk.
+		 */
+		export const onWillSaveTextDocument: Event<TextDocumentWillSaveEvent>;
+
 		/**
 		 * An event that is emitted when a [text document](#TextDocument) is saved to disk.
 		 */
diff --git a/src/vs/workbench/api/node/extHost.api.impl.ts b/src/vs/workbench/api/node/extHost.api.impl.ts
index 163fd0a8e6a695b0912c589dc1447c04da45cd58..2615b5447b864be4b4ff2cc9fa6175d62008fb12 100644
--- a/src/vs/workbench/api/node/extHost.api.impl.ts
+++ b/src/vs/workbench/api/node/extHost.api.impl.ts
@@ -103,6 +103,7 @@ export class ExtHostAPIImplementation {
 
 		const extHostHeapMonitor = col.define(ExtHostContext.ExtHostHeapService).set<ExtHostHeapService>(new ExtHostHeapService());
 		const extHostDocuments = col.define(ExtHostContext.ExtHostDocuments).set<ExtHostDocuments>(new ExtHostDocuments(threadService));
+		const estHostDocumentSaveParticipant = col.define(ExtHostContext.ExtHostDocumentSaveParticipant).set<ExtHostDocumentSaveParticipant>(new ExtHostDocumentSaveParticipant(extHostDocuments, threadService.get(MainContext.MainThreadWorkspace)));
 		const extHostEditors = col.define(ExtHostContext.ExtHostEditors).set<ExtHostEditors>(new ExtHostEditors(threadService, extHostDocuments));
 		const extHostCommands = col.define(ExtHostContext.ExtHostCommands).set<ExtHostCommands>(new ExtHostCommands(threadService, extHostEditors));
 		const extHostConfiguration = col.define(ExtHostContext.ExtHostConfiguration).set<ExtHostConfiguration>(new ExtHostConfiguration(threadService.get(MainContext.MainThreadConfiguration)));
@@ -111,7 +112,6 @@ export class ExtHostAPIImplementation {
 		const extHostFileSystemEvent = col.define(ExtHostContext.ExtHostFileSystemEventService).set<ExtHostFileSystemEventService>(new ExtHostFileSystemEventService());
 		const extHostQuickOpen = col.define(ExtHostContext.ExtHostQuickOpen).set<ExtHostQuickOpen>(new ExtHostQuickOpen(threadService));
 		const extHostTerminalService = col.define(ExtHostContext.ExtHostTerminalService).set<ExtHostTerminalService>(new ExtHostTerminalService(threadService));
-		col.define(ExtHostContext.ExtHostDocumentSaveParticipant).set<ExtHostDocumentSaveParticipant>(new ExtHostDocumentSaveParticipant(extHostDocuments, threadService.get(MainContext.MainThreadWorkspace)));
 		col.define(ExtHostContext.ExtHostExtensionService).set(extensionService);
 
 		col.finish(false, threadService);
@@ -325,6 +325,9 @@ export class ExtHostAPIImplementation {
 			onDidSaveTextDocument: (listener, thisArgs?, disposables?) => {
 				return extHostDocuments.onDidSaveDocument(listener, thisArgs, disposables);
 			},
+			onWillSaveTextDocument: (listener, thisArgs?, disposables?) => {
+				return estHostDocumentSaveParticipant.onWillSaveTextDocumentEvent(listener, thisArgs, disposables);
+			},
 			onDidChangeConfiguration: (listener: () => any, thisArgs?: any, disposables?: extHostTypes.Disposable[]) => {
 				return extHostConfiguration.onDidChangeConfiguration(listener, thisArgs, disposables);
 			},
diff --git a/src/vs/workbench/api/node/extHostDocumentSaveParticipant.ts b/src/vs/workbench/api/node/extHostDocumentSaveParticipant.ts
index 319ae064189db90328fa5266c7c39abeb8fea646..e8a551d103a959f8394d6c233fd500c499d9d049 100644
--- a/src/vs/workbench/api/node/extHostDocumentSaveParticipant.ts
+++ b/src/vs/workbench/api/node/extHostDocumentSaveParticipant.ts
@@ -16,10 +16,6 @@ import {fromRange} from 'vs/workbench/api/node/extHostTypeConverters';
 import {IResourceEdit} from 'vs/editor/common/services/bulkEdit';
 import {ExtHostDocuments} from 'vs/workbench/api/node/extHostDocuments';
 
-export interface TextDocumentWillSaveEvent {
-	document: vscode.TextDocument;
-	waitUntil(t: Thenable<any | vscode.TextEdit[]>): void;
-}
 
 export class ExtHostDocumentSaveParticipant extends ExtHostDocumentSaveParticipantShape {
 
@@ -37,7 +33,7 @@ export class ExtHostDocumentSaveParticipant extends ExtHostDocumentSaveParticipa
 		this._callbacks.dispose();
 	}
 
-	get onWillSaveTextDocumentEvent(): Event<TextDocumentWillSaveEvent> {
+	get onWillSaveTextDocumentEvent(): Event<vscode.TextDocumentWillSaveEvent> {
 		return (listener, thisArg, disposables) => {
 			this._callbacks.add(listener, thisArg);
 			const result = { dispose: () => this._callbacks.remove(listener, thisArg) };
@@ -65,7 +61,7 @@ export class ExtHostDocumentSaveParticipant extends ExtHostDocumentSaveParticipa
 
 		const {version} = document;
 
-		const event = Object.freeze(<TextDocumentWillSaveEvent> {
+		const event = Object.freeze(<vscode.TextDocumentWillSaveEvent> {
 			document,
 			waitUntil(p: Thenable<any | vscode.TextEdit[]>) {
 				if (Object.isFrozen(promises)) {
diff --git a/src/vs/workbench/test/node/api/extHostDocumentSaveParticipant.test.ts b/src/vs/workbench/test/node/api/extHostDocumentSaveParticipant.test.ts
index 60f6d16f6885066b868cd3cefc4a12b27174b57f..2ed91e8f17a212369401ca355ccc3e3cb9dcab03 100644
--- a/src/vs/workbench/test/node/api/extHostDocumentSaveParticipant.test.ts
+++ b/src/vs/workbench/test/node/api/extHostDocumentSaveParticipant.test.ts
@@ -10,7 +10,7 @@ import {TPromise} from 'vs/base/common/winjs.base';
 import {ExtHostDocuments} from 'vs/workbench/api/node/extHostDocuments';
 import {TextEdit, Position} from 'vs/workbench/api/node/extHostTypes';
 import {MainThreadWorkspaceShape} from 'vs/workbench/api/node/extHost.protocol';
-import {ExtHostDocumentSaveParticipant, TextDocumentWillSaveEvent} from 'vs/workbench/api/node/extHostDocumentSaveParticipant';
+import {ExtHostDocumentSaveParticipant} from 'vs/workbench/api/node/extHostDocumentSaveParticipant';
 import {OneGetThreadService} from './testThreadService';
 import * as EditorCommon from 'vs/editor/common/editorCommon';
 import {IResourceEdit} from 'vs/editor/common/services/bulkEdit';
@@ -52,7 +52,7 @@ suite('ExtHostDocumentSaveParticipant', () => {
 	test('event delivery', () => {
 		const participant = new ExtHostDocumentSaveParticipant(documents, workspace);
 
-		let event: TextDocumentWillSaveEvent;
+		let event: vscode.TextDocumentWillSaveEvent;
 		let sub = participant.onWillSaveTextDocumentEvent(function (e) {
 			event = e;
 		});
@@ -68,7 +68,7 @@ suite('ExtHostDocumentSaveParticipant', () => {
 	test('event delivery, immutable', () => {
 		const participant = new ExtHostDocumentSaveParticipant(documents, workspace);
 
-		let event: TextDocumentWillSaveEvent;
+		let event: vscode.TextDocumentWillSaveEvent;
 		let sub = participant.onWillSaveTextDocumentEvent(function (e) {
 			event = e;
 		});
@@ -145,7 +145,7 @@ suite('ExtHostDocumentSaveParticipant', () => {
 			e.waitUntil(TPromise.wrapError('dddd'));
 		});
 
-		let event: TextDocumentWillSaveEvent;
+		let event: vscode.TextDocumentWillSaveEvent;
 		let sub2 = participant.onWillSaveTextDocumentEvent(function (e) {
 			event = e;
 		});