diff --git a/CHANGELOG.md b/CHANGELOG.md
index 057b4f29..9dbca0b8 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -13,6 +13,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 ### Changed
 
 ### Fixed
+- chromeless can now be imported into TypeScript projects with activated `strictNullChecks` compiler option [#154](https://github.com/graphcool/chromeless/pull/154) @clebert
 
 
 ## [1.1.0] - 2017-08-02
diff --git a/src/api.ts b/src/api.ts
index 603bffac..eb28e32f 100644
--- a/src/api.ts
+++ b/src/api.ts
@@ -53,8 +53,8 @@ export default class Chromeless<T extends any> implements Promise<T> {
   readonly [Symbol.toStringTag]: 'Promise'
 
   then<U>(
-    onFulfill: (value: T) => U | PromiseLike<U>,
-    onReject?: (error: any) => U | PromiseLike<U>,
+    onFulfill?: ((value: T) => U | PromiseLike<U>) | null,
+    onReject?: ((error: any) => U | PromiseLike<U>) | null,
   ): Promise<U> {
     return this.lastReturnPromise.then(onFulfill, onReject) as Promise<U>
   }