diff --git a/lib/eventsource.js b/lib/eventsource.js
index 160b0b0..082656f 100644
--- a/lib/eventsource.js
+++ b/lib/eventsource.js
@@ -298,6 +298,10 @@ Object.defineProperty(EventSource, 'CONNECTING', {enumerable: true, value: 0})
 Object.defineProperty(EventSource, 'OPEN', {enumerable: true, value: 1})
 Object.defineProperty(EventSource, 'CLOSED', {enumerable: true, value: 2})
 
+EventSource.prototype.CONNECTING = 0
+EventSource.prototype.OPEN = 1
+EventSource.prototype.CLOSED = 2
+
 /**
  * Emulates the W3C Browser based WebSocket interface using addEventListener.
  *
diff --git a/test/eventsource_test.js b/test/eventsource_test.js
index 36aa3ea..2c25a4d 100644
--- a/test/eventsource_test.js
+++ b/test/eventsource_test.js
@@ -762,6 +762,18 @@ describe('readyState', function () {
     assert.equal(2, EventSource.CLOSED)
   })
 
+  it('has readystate constants on instances', function (done) {
+    var es = new EventSource('http://localhost:' + _port)
+    assert.equal(EventSource.CONNECTING, es.CONNECTING, 'constant CONNECTING missing/invalid')
+    assert.equal(EventSource.OPEN, es.OPEN, 'constant OPEN missing/invalid')
+    assert.equal(EventSource.CLOSED, es.CLOSED, 'constant CLOSED missing/invalid')
+
+    es.onerror = function () {
+      es.close()
+      done()
+    }
+  })
+
   it('is CONNECTING before connection has been established', function (done) {
     var es = new EventSource('http://localhost:' + _port)
     assert.equal(EventSource.CONNECTING, es.readyState)