openApiGenerate treating .yaml as .json

My openapi.yaml is:

openapi: "3.0.3"
info:
  title: Miit API
  version: "1.0"
servers:
  - url: https://staging1.miit.co:8443/apiv2
    description: staging (test) server
paths:
  /profile:
    get:
      description: The requested user's profile, if it exist
      parameters:
        - name: id
          in: query
          description: user id.
          required: true
          schema:
            type: integer
            format: int32
            minimum: 1
      responses:
        '200':
          description: profile body
          content:
            application/json:
              schema:
                $ref: 'schemae/profileGet.yaml'
        '404':
          description: No such profile OR access denied
          content:
            application/json:
              schema:
                type: object

components:
  securitySchemes:
    basicAuth:
      type: http
      scheme: basic

security:
  - basicAuth: []

and my schemae/profileGet.yaml starts:

type: object
properties:
 username:
   type: string
 description:
   type: string

but when I run ./gradlew openApiGenerate it fails with:

> Task :openApiGenerate
failed to read resource listing
com.fasterxml.jackson.core.JsonParseException: Unrecognized token 'type': was expecting (JSON String, Number, Array, Object or token 'null', 'true' or 'false')
at [Source: (String)"type: object
properties:
[...]

What could possibly be causing the generator to treat profileGet.yaml as JSON ???