Typescript: Property 'DB' does not exist on type 'Global'

In my src/app.ts, I have:

import DB from '../models'

And in src/models/index.ts, I have:

export default (() => {
    if (global.DB) {
        return global.DB
    }
    ...
    // Do some other stuff
    return something

My typings/global.d.ts has:

declare namespace NodeJS {
    export interface Global {
        DB: any;
    }
}

declare var DB: any;

And finally, my tsconfig.json has:

{
    "compilerOptions": {
        "outDir": "./built",
        "allowJs": true,
        "target": "es6",
        "esModuleInterop": true,
        "sourceMap": true
    },
    "include": [
        "./src/**/*"
    ],
    "files": [
        "typings/*"
    ]
}

But I still get the error:

Error: src/models/index.ts(7,16): error TS2339: Property 'DB' does not exist on type 'Global'.

What am I doing incorrectly?

from Typescript: Property 'DB' does not exist on type 'Global'