**TypeScript Version:** 2.2.1 / nightly (2.2.0-dev.201xxxxx) **Code** [By the spec](https://url.spec.whatwg.org/#interface-urlsearchparams): ```ts let params = new URLSearchParams({key: "730d67"}) params.toString() // "key=730d67" ``` **Expected behavior:** The example should work. **Actual behavior:** Error: Argument of type '{ key: string }' is not assignable to parameter of type 'string | URLSearchParams`