.d.ts not compiling after TypeScript 2.6.1

I was using TypeScript version 2.5 with this ambient module for suncalc package:

// Note: incomplete
// https://www.npmjs.com/package/suncalc

declare module "suncalc" {
  interface suncalcResult {
    solarNoon: Date;
    nadir: Date;
    sunrise: Date;
    sunset: Date;
    sunriseEnd: Date;
    sunsetStart: Date;
    dawn: Date;
    dusk: Date;
    nauticalDawn: Date;
    nauticalDusk: Date;
    nightEnd: Date;
    night: Date;
    goldenHourEnd: Date;
    goldenHour: Date;
  }

  function sunCalc(date: Date, latitude: number, longitude: number): suncalcResult;

  export = { // COMPLAINING HERE <--------------------------- line 24
    getTimes: sunCalc
  };
}

In TypeScript 2.5, I got this file called suncalc.d.ts and compiled with no error. When I upgraded to 2.6, it started to blame:

message: 'The expression of an export assignment must be an identifier or qualified name in an ambient context.'
at: '24,12'
source: 'ts'

However, in the changelog of TypeScript there is nothing about changes in ambient modules.

Why is not compiling now? How should I write the export in TS2.6?