Can't extend interface in module

[jon49]

declare module A {
    interface B {
        a: string
        b: number
    }
}

interface C extends A.B {}

Results in

{
  "A.B": {
    "id": "A.B",
    "type": "object",
    "properties": {
      "a": {
        "type": "string"
      },
      "b": {
        "type": "number"
      }
    },
    "required": [
      "a",
      "b"
    ],
    "additionalProperties": false
  },
  "C": {
    "id": "C",
    "type": "object",
    "properties": {},
    "additionalProperties": false
  }
}

As you can see, C has no properties when it should inherit A.B.