diff --git a/src/monaco.contribution.ts b/src/monaco.contribution.ts
index 0e9fcfb7..c038d4b5 100644
--- a/src/monaco.contribution.ts
+++ b/src/monaco.contribution.ts
@@ -208,11 +208,11 @@ const javascriptDefaults = new LanguageServiceDefaultsImpl(
 	{ allowNonTsExtensions: true, allowJs: true, target: ScriptTarget.Latest },
 	{ noSemanticValidation: true, noSyntaxValidation: false });
 
-function getTypeScriptWorker(): Promise<any> {
+function getTypeScriptWorker(): Promise<(...uris: monaco.Uri[]) => Promise<monaco.languages.typescript.TypeScriptWorker>> {
 	return getMode().then(mode => mode.getTypeScriptWorker());
 }
 
-function getJavaScriptWorker(): Promise<any> {
+function getJavaScriptWorker(): Promise<(...uris: monaco.Uri[]) => Promise<monaco.languages.typescript.TypeScriptWorker>> {
 	return getMode().then(mode => mode.getJavaScriptWorker());
 }
 
diff --git a/src/monaco.d.ts b/src/monaco.d.ts
index 853bbaf4..d17315d7 100644
--- a/src/monaco.d.ts
+++ b/src/monaco.d.ts
@@ -377,11 +377,11 @@ declare module monaco.languages.typescript {
         getCodeFixesAtPosition(fileName: string, start: number, end: number, errorCodes: number[], formatOptions: any): Promise<ReadonlyArray<any>>;
     }
 
-    export var typescriptVersion: string;
+    export const typescriptVersion: string;
 
-    export var typescriptDefaults: LanguageServiceDefaults;
-    export var javascriptDefaults: LanguageServiceDefaults;
+    export const typescriptDefaults: LanguageServiceDefaults;
+    export const javascriptDefaults: LanguageServiceDefaults;
 
-    export var getTypeScriptWorker: () => Promise<(first: Uri, ...more: Uri[]) => Promise<TypeScriptWorker>>;
-    export var getJavaScriptWorker: () => Promise<(first: Uri, ...more: Uri[]) => Promise<TypeScriptWorker>>;
+    export const getTypeScriptWorker: () => Promise<(...uris: Uri[]) => Promise<TypeScriptWorker>>;
+    export const getJavaScriptWorker: () => Promise<(...uris: Uri[]) => Promise<TypeScriptWorker>>;
 }
diff --git a/src/tsMode.ts b/src/tsMode.ts
index 8842fd63..efc95412 100644
--- a/src/tsMode.ts
+++ b/src/tsMode.ts
@@ -11,8 +11,8 @@ import * as languageFeatures from './languageFeatures';
 
 import Uri = monaco.Uri;
 
-let javaScriptWorker: (first: Uri, ...more: Uri[]) => Promise<TypeScriptWorker>;
-let typeScriptWorker: (first: Uri, ...more: Uri[]) => Promise<TypeScriptWorker>;
+let javaScriptWorker: (...uris: Uri[]) => Promise<TypeScriptWorker>;
+let typeScriptWorker: (...uris: Uri[]) => Promise<TypeScriptWorker>;
 
 export function setupTypeScript(defaults: LanguageServiceDefaultsImpl): void {
 	typeScriptWorker = setupMode(
@@ -28,7 +28,7 @@ export function setupJavaScript(defaults: LanguageServiceDefaultsImpl): void {
 	);
 }
 
-export function getJavaScriptWorker(): Promise<(first: Uri, ...more: Uri[]) => Promise<TypeScriptWorker>> {
+export function getJavaScriptWorker(): Promise<(...uris: Uri[]) => Promise<TypeScriptWorker>> {
 	return new Promise((resolve, reject) => {
 		if (!javaScriptWorker) {
 			return reject("JavaScript not registered!");
@@ -38,7 +38,7 @@ export function getJavaScriptWorker(): Promise<(first: Uri, ...more: Uri[]) => P
 	});
 }
 
-export function getTypeScriptWorker(): Promise<(first: Uri, ...more: Uri[]) => Promise<TypeScriptWorker>> {
+export function getTypeScriptWorker(): Promise<(...uris: Uri[]) => Promise<TypeScriptWorker>> {
 	return new Promise((resolve, reject) => {
 		if (!typeScriptWorker) {
 			return reject("TypeScript not registered!");
@@ -48,11 +48,11 @@ export function getTypeScriptWorker(): Promise<(first: Uri, ...more: Uri[]) => P
 	});
 }
 
-function setupMode(defaults: LanguageServiceDefaultsImpl, modeId: string): (first: Uri, ...more: Uri[]) => Promise<TypeScriptWorker> {
+function setupMode(defaults: LanguageServiceDefaultsImpl, modeId: string): (...uris: Uri[]) => Promise<TypeScriptWorker> {
 
 	const client = new WorkerManager(modeId, defaults);
-	const worker = (first: Uri, ...more: Uri[]): Promise<TypeScriptWorker> => {
-		return client.getLanguageServiceWorker(...[first].concat(more));
+	const worker = (...uris: Uri[]): Promise<TypeScriptWorker> => {
+		return client.getLanguageServiceWorker(...uris);
 	};
 
 	monaco.languages.registerCompletionItemProvider(modeId, new languageFeatures.SuggestAdapter(worker));
diff --git a/src/tsWorker.ts b/src/tsWorker.ts
index b3cee653..32b9a6bb 100644
--- a/src/tsWorker.ts
+++ b/src/tsWorker.ts
@@ -20,7 +20,7 @@ const ES6_LIB = {
 	CONTENTS: lib_es6_dts
 };
 
-export class TypeScriptWorker implements ts.LanguageServiceHost {
+export class TypeScriptWorker implements ts.LanguageServiceHost, monaco.languages.typescript.TypeScriptWorker {
 
 	// --- model sync -----------------------
 
@@ -123,7 +123,7 @@ export class TypeScriptWorker implements ts.LanguageServiceHost {
 
 	// --- language features
 
-	private static clearFiles(diagnostics: ts.Diagnostic[]) {
+	private static clearFiles(diagnostics: ts.Diagnostic[]): monaco.languages.typescript.Diagnostic[] {
 		// Clear the `file` field, which cannot be JSON'yfied because it
 		// contains cyclic data structures.
 		diagnostics.forEach(diag => {
@@ -133,30 +133,27 @@ export class TypeScriptWorker implements ts.LanguageServiceHost {
 				related.forEach(diag2 => diag2.file = undefined);
 			}
 		});
+		return <monaco.languages.typescript.Diagnostic[]>diagnostics;
 	}
 
-	getSyntacticDiagnostics(fileName: string): Promise<ts.Diagnostic[]> {
+	getSyntacticDiagnostics(fileName: string): Promise<monaco.languages.typescript.Diagnostic[]> {
 		const diagnostics = this._languageService.getSyntacticDiagnostics(fileName);
-		TypeScriptWorker.clearFiles(diagnostics);
-		return Promise.resolve(diagnostics);
+		return Promise.resolve(TypeScriptWorker.clearFiles(diagnostics));
 	}
 
-	getSemanticDiagnostics(fileName: string): Promise<ts.Diagnostic[]> {
+	getSemanticDiagnostics(fileName: string): Promise<monaco.languages.typescript.Diagnostic[]> {
 		const diagnostics = this._languageService.getSemanticDiagnostics(fileName);
-		TypeScriptWorker.clearFiles(diagnostics);
-		return Promise.resolve(diagnostics);
+		return Promise.resolve(TypeScriptWorker.clearFiles(diagnostics));
 	}
 
-	getSuggestionDiagnostics(fileName: string): Promise<ts.DiagnosticWithLocation[]> {
+	getSuggestionDiagnostics(fileName: string): Promise<monaco.languages.typescript.Diagnostic[]> {
 		const diagnostics = this._languageService.getSuggestionDiagnostics(fileName);
-		TypeScriptWorker.clearFiles(diagnostics);
-		return Promise.resolve(diagnostics);
+		return Promise.resolve(TypeScriptWorker.clearFiles(diagnostics));
 	}
 
-	getCompilerOptionsDiagnostics(fileName: string): Promise<ts.Diagnostic[]> {
+	getCompilerOptionsDiagnostics(fileName: string): Promise<monaco.languages.typescript.Diagnostic[]> {
 		const diagnostics = this._languageService.getCompilerOptionsDiagnostics();
-		TypeScriptWorker.clearFiles(diagnostics);
-		return Promise.resolve(diagnostics);
+		return Promise.resolve(TypeScriptWorker.clearFiles(diagnostics));
 	}
 
 	getCompletionsAtPosition(fileName: string, position: number): Promise<ts.CompletionInfo | undefined> {