diff --git a/package.json b/package.json
index fb5b11f..1fc425f 100644
--- a/package.json
+++ b/package.json
@@ -28,6 +28,7 @@
   },
   "devDependencies": {
     "browserify": "^9.0.0",
-    "mocha": "^2.2.0"
+    "mocha": "^2.2.0",
+    "mock-require": "^1.0.5"
   }
 }
diff --git a/test/index.js b/test/index.js
index 9cbff2c..b201882 100644
--- a/test/index.js
+++ b/test/index.js
@@ -1,4 +1,10 @@
 var assert = require('assert')
+var mock = require('mock-require')
+
+mock('randombytes', function(size) {
+  return new Buffer('qwertyuiopasdfghjklzxcvbnm[];,./'.slice(0, size))
+})
+
 var BIP39 = require('../index.js')
 
 var wordlists = {
@@ -63,6 +69,10 @@ describe('BIP39', function() {
       assert.equal(words.length, 9)
     })
 
+    it('defaults to randombytes for the RNG', function() {
+      assert.equal(BIP39.generateMnemonic(32), 'imitate robot frequent')
+    })
+
     it('allows a custom RNG to be used', function() {
       var rng = function(size) {
         var buffer = new Buffer(size)