npm-dts: Doesn't seem to work with JavaScript source files

Tried running this with a small test module and I get this:

> npm-dts generate -r . -e lib/index.js -L verbose

[npm-dts] [info] :  _________________________________________ 
[npm-dts] [info] : |                                         |
[npm-dts] [info] : |                                         |
[npm-dts] [info] : |          npm-dts v1.1.10                |
[npm-dts] [info] : |          by Vytenis Urbonavičius        |
[npm-dts] [info] : |                                         |
[npm-dts] [info] : |_________________________________________|
[npm-dts] [info] :                                            
[npm-dts] [info] : Generating declarations for "/Users/{someone}/Workspace/sandbox/docs"...
[npm-dts] [verbose] : Locating OS Temporary Directory...
[npm-dts] [verbose] : OS Temporary Directory was located!
[npm-dts] [verbose] : Will now reset "tmp" directory...
[npm-dts] [verbose] : Cleaning up "tmp" directory...
[npm-dts] [verbose] : "tmp" directory was cleaned!
[npm-dts] [verbose] : Preparing "tmp" directory...
[npm-dts] [verbose] : "tmp" directory was prepared!
[npm-dts] [verbose] : Generating per-file typings using TSC...
[npm-dts] [error] : Generation of index.d.ts has failed!
[npm-dts] [verbose] : Cleaning up "tmp" directory...
[npm-dts] [verbose] : "tmp" directory was cleaned!
[npm-dts] [verbose] : Deleting OS Temporary Directory...
[npm-dts] [verbose] : OS Temporary Directory was deleted!
[npm-dts] [error] : Generation failed!

My tsconfig.json is:

{
  "compilerOptions": {
    "allowJs": true,
    "checkJs": true,
    "strict": true,
    "strictNullChecks": true,
    "outDir": "build"
  },
  "include": [
    "lib"
  ]
}