diff --git a/src/tsconfig.strictNullChecks.json b/src/tsconfig.strictNullChecks.json
index 59f6328c061..e87e4dc83eb 100644
--- a/src/tsconfig.strictNullChecks.json
+++ b/src/tsconfig.strictNullChecks.json
@@ -6,7 +6,10 @@
 	},
 	"include": [
 		"./typings",
-		"./vs/base/common/iterator.ts"
+		"./vs/base/common/charCode.ts",
+		"./vs/base/common/iterator.ts",
+		"./vs/base/common/platform.ts",
+		"./vs/base/common/uri.ts"
 	],
 	"exclude": [
 		"./typings/require-monaco.d.ts"
diff --git a/src/vs/base/common/platform.ts b/src/vs/base/common/platform.ts
index 9e3496c8160..4b703fc900a 100644
--- a/src/vs/base/common/platform.ts
+++ b/src/vs/base/common/platform.ts
@@ -8,9 +8,9 @@ let _isMacintosh = false;
 let _isLinux = false;
 let _isNative = false;
 let _isWeb = false;
-let _locale: string = undefined;
-let _language: string = undefined;
-let _translationsConfigFile: string = undefined;
+let _locale: string | undefined = undefined;
+let _language: string | undefined = undefined;
+let _translationsConfigFile: string | undefined = undefined;
 
 interface NLSConfig {
 	locale: string;
@@ -129,7 +129,7 @@ export const translationsConfigFile = _translationsConfigFile;
 const _globals = (typeof self === 'object' ? self : typeof global === 'object' ? global : {} as any);
 export const globals: any = _globals;
 
-let _setImmediate: (callback: (...args: any[]) => void) => number = null;
+let _setImmediate: ((callback: (...args: any[]) => void) => number) | null = null;
 export function setImmediate(callback: (...args: any[]) => void): number {
 	if (_setImmediate === null) {
 		if (globals.setImmediate) {
@@ -140,7 +140,7 @@ export function setImmediate(callback: (...args: any[]) => void): number {
 			_setImmediate = globals.setTimeout.bind(globals);
 		}
 	}
-	return _setImmediate(callback);
+	return _setImmediate!(callback);
 }
 
 export const enum OperatingSystem {
diff --git a/src/vs/base/common/uri.ts b/src/vs/base/common/uri.ts
index 3ce4b48c95b..c0d3423e240 100644
--- a/src/vs/base/common/uri.ts
+++ b/src/vs/base/common/uri.ts
@@ -141,7 +141,7 @@ export class URI implements UriComponents {
 	/**
 	 * @internal
 	 */
-	protected constructor(scheme: string, authority: string, path: string, query: string, fragment: string);
+	protected constructor(scheme: string, authority?: string, path?: string, query?: string, fragment?: string);
 
 	/**
 	 * @internal
@@ -386,8 +386,8 @@ interface UriState extends UriComponents {
 // tslint:disable-next-line:class-name
 class _URI extends URI {
 
-	_formatted: string = null;
-	_fsPath: string = null;
+	_formatted: string | null = null;
+	_fsPath: string | null = null;
 
 	get fsPath(): string {
 		if (!this._fsPath) {
@@ -465,7 +465,7 @@ const encodeTable: { [ch: number]: string } = {
 };
 
 function encodeURIComponentFast(uriComponent: string, allowSlash: boolean, firstPos: number = 0): string {
-	let res: string = undefined;
+	let res: string | undefined = undefined;
 	let nativeEncodePos = -1;
 
 	for (let pos = firstPos; pos < uriComponent.length; pos++) {
@@ -526,7 +526,7 @@ function encodeURIComponentFast(uriComponent: string, allowSlash: boolean, first
 }
 
 function encodeURIComponentMinimal(path: string): string {
-	let res: string = undefined;
+	let res: string | undefined = undefined;
 	for (let pos = 0; pos < path.length; pos++) {
 		let code = path.charCodeAt(pos);
 		if (code === CharCode.Hash || code === CharCode.QuestionMark) {