diff --git a/src/api/autorun.ts b/src/api/autorun.ts
index 43a482db8..736fba724 100644
--- a/src/api/autorun.ts
+++ b/src/api/autorun.ts
@@ -197,7 +197,7 @@ export function reaction<T>(expression: (r: IReactionPublic) => T, effect: (arg:
 	let nextValue: T;
 
 	const r = new Reaction(opts.name, () => {
-		if (opts.delay < 1) {
+		if ((opts.delay as any) < 1) {
 			reactionRunner();
 		} else if (!isScheduled) {
 			isScheduled = true;
diff --git a/src/types/observablevalue.ts b/src/types/observablevalue.ts
index 31bdf2314..05ad1a50a 100644
--- a/src/types/observablevalue.ts
+++ b/src/types/observablevalue.ts
@@ -127,4 +127,4 @@ export class ObservableValue<T> extends BaseAtom implements IObservableValue<T>,
 
 ObservableValue.prototype[primitiveSymbol()] = ObservableValue.prototype.valueOf;
 
-export const isObservableValue = createInstanceofPredicate("ObservableValue", ObservableValue);
+export var isObservableValue = createInstanceofPredicate("ObservableValue", ObservableValue) as (x: any) => x is IObservableValue<any>;
diff --git a/src/utils/decorators.ts b/src/utils/decorators.ts
index 4c4222a6c..181543fc1 100644
--- a/src/utils/decorators.ts
+++ b/src/utils/decorators.ts
@@ -28,7 +28,7 @@ export function createClassPropertyDecorator(
 	 */
 	allowCustomArguments: boolean
 ): any {
-	function classPropertyDecorator(target: any, key: string, descriptor, customArgs?: IArguments, argLen?: number) {
+	function classPropertyDecorator(target: any, key: string, descriptor, customArgs?: IArguments, argLen: number = 0) {
 		invariant(allowCustomArguments || quacksLikeADecorator(arguments), "This function is a decorator, but it wasn't invoked like a decorator");
 		if (!descriptor) {
 			// typescript (except for getter / setters)
diff --git a/test/babel/babel-tests.js b/test/babel/babel-tests.js
index 490db8726..45a3629a2 100644
--- a/test/babel/babel-tests.js
+++ b/test/babel/babel-tests.js
@@ -1,8 +1,8 @@
 import {
     observable, computed, transaction, autorun, extendObservable, action,
-	isObservableObject, observe, isObservable, spy, isAction,
-    default as mobx
+	isObservableObject, observe, isObservable, spy, isAction, useStrict
 } from "../";
+import * as mobx from "../"
 
 var test = require('tape')
 
@@ -334,13 +334,13 @@ test("custom action decorator on field (babel)", function(t) {
 });
 
 test("267 (babel) should be possible to declare properties observable outside strict mode", t => {
-	mobx.useStrict(true);
+	useStrict(true);
 
 	class Store {
 		@observable timer;
 	}
 
-	mobx.useStrict(false);
+	useStrict(false);
 	t.end();
 })