diff --git a/README.md b/README.md
index c19ac20..9be9114 100644
--- a/README.md
+++ b/README.md
@@ -51,8 +51,8 @@ type XhrOptions = String | {
     method: String?,
     timeout: Number?,
     headers: Object?,
-    body: String?,
-    json: Object?,
+    body: String||Object?,
+    json: Boolean?,
     username: String?,
     password: String?,
     withCredentials: Boolean?,
@@ -148,6 +148,8 @@ Pass in body to be send across the [`XMLHttpRequest`][3].
     Generally should be a string. But anything that's valid as
     a parameter to [`XMLHttpRequest.send`][1] should work  (Buffer for file, etc.).
 
+If `options.json` is `true`, then this must be a JSON-serializable object.
+
 ### `options.uri` or `options.url`
 
 The uri to send a request to. Passed to [`XMLHttpRequest.open`][2]. `options.url` and `options.uri` are aliases for each other.
@@ -163,8 +165,7 @@ Number of miliseconds to wait for response. Defaults to 0 (no timeout). Ignored
 
 ### `options.json`
 
-A valid JSON serializable value to be send to the server. If this
-    is set then we serialize the value and use that as the body.
+If set to `true` then we serialize the value of `options.body` and send that as the request body.
     We also set the Content-Type to `"application/json"`.
 
 Additionally the response body is parsed as JSON
@@ -195,9 +196,11 @@ Pass an `XMLHttpRequest` object (or something that acts like one) to use instead
   - See `options.json` - you can set it to `true` on a GET request to tell `xhr` to parse the response body.
   - Without `options.json` body is returned as-is (a string or when `responseType` is set and the browser supports it - a result of parsing JSON or XML)
 - How do I send an object or array as POST body?
-  - `options.body` should be a string. You need to serialize your object before passing to `xhr` for sending.
-  - To serialize to JSON you can use
-   `options.json` instead of `options.body` for convenience - then `xhr` will do the serialization and set content-type accordingly.
+  - `options.body` should be a string or any other value that's valid as
+  a parameter to [`XMLHttpRequest.send`][1]. Any other value needs to
+  be serialized before passed to `xhr` for sending.
+  - To serialize to JSON you can set
+   `options.json` to `true` for convenience - then `xhr` will do the serialization and set content-type accordingly.
 - Where's stream API? `.pipe()` etc.
   - Not implemented. You can't reasonably have that in the browser.
 
diff --git a/index.js b/index.js
index a1deb4d..16d73cf 100644
--- a/index.js
+++ b/index.js
@@ -158,12 +158,12 @@ function _createXHR(options) {
     var isJson = false
     var timeoutTimer
 
-    if ("json" in options) {
+    if (options.json === true) {
         isJson = true
         headers["accept"] || headers["Accept"] || (headers["Accept"] = "application/json") //Don't override existing accept header declared by user
         if (method !== "GET" && method !== "HEAD") {
             headers["content-type"] || headers["Content-Type"] || (headers["Content-Type"] = "application/json") //Don't override existing accept header declared by user
-            body = JSON.stringify(options.json)
+            body = JSON.stringify(options.body)
         }
     }
 
diff --git a/test/index.js b/test/index.js
index 689bff3..3fd1171 100644
--- a/test/index.js
+++ b/test/index.js
@@ -189,6 +189,16 @@ test("xhr[method] get, put, post, patch with url shorthands", function(assert) {
     })
 })
 
+test("json encoded request body", function(assert) {
+    xhr.post("/mock/echo", {
+        json: true,
+        body: {foo: "bar"}
+    }, function(err, resp, body) {
+        assert.equal(resp.rawRequest.headers["Content-Type"], "application/json")
+        assert.deepEqual(body, {foo: "bar"})
+        assert.end()
+    })
+})
 
 test("xhr[method] get, put, post, patch with url shorthands and options", function(assert) {
     var i = 0
diff --git a/test/mock-server.js b/test/mock-server.js
index 5d7d57d..913bdc2 100644
--- a/test/mock-server.js
+++ b/test/mock-server.js
@@ -6,6 +6,15 @@ module.exports = function (req, res) {
     } else if (req.url === '/mock/no-content') {
         res.statusCode = 204
         res.end('')
+    } else if (req.url === '/mock/echo') {
+        var body = []
+        req.on('data', function(chunk) {
+            body.push(chunk)
+        })
+        req.on('end', function() {
+            res.statusCode = 200
+            res.end(Buffer.concat(body).toString())
+        })
     } else if (req.url === '/mock/timeout') {
         setTimeout(function() {
             res.statusCode = 200