[ERROR] ReferenceError: Error when compiling Harp

I am developing a benchmark of the page generation time of the different SSGs, harp is not conducting as expected.

$harp compile
{
  "source": "EJS",
  "dest": "HTML",
  "filename": "/opt/harp/src/_partials/head.ejs",
  "lineno": 3,
  "name": "ReferenceError",
  "message": "/opt/harp/src/_layout.ejs:3\n    1| <!DOCTYPE html>\n    2| <html>\n >> 3|   <%- partial( \"_partials/head\" ) %>\n    4|   <body>\n    5|     <%- partial( \"_partials/github\" ) %>\n    6|     <%- partial( \"_partials/header\" ) %>\n\nsite is not defined",
  "stack": "<head>\n  <meta charset=\"utf-8\">\n  <title><%- page.title %> | <%- site.title %></title>\n\n  <!-- CSS -->\n  <link rel=\"stylesheet\" href=\"http://fonts.googleapis.com/css?family=PT+Serif:400,400italic,700|PT+Sans:400\">\n  <link rel=\"stylesheet\" href=\"<%- site.path %>/css/style.css\">\n</head>\n",
  "path": "/opt/harp/src/_layout.ejs"
}

Data:

sintaxi / harp

[ERROR] ReferenceError: Error when compiling Harp #652