diff --git a/index.js b/index.js
index 19a8211..f0f2743 100644
--- a/index.js
+++ b/index.js
@@ -35,9 +35,9 @@ BIP39.prototype.entropyToMnemonic = function(entropy) {
 
 BIP39.prototype.generateMnemonic = function(strength, rng) {
   strength = strength || 128
-  rng = rng || secureRandom
+  rng = rng || secureRandom.randomBuffer
 
-  var hex = rng.randomBuffer(strength / 8).toString('hex')
+  var hex = rng(strength / 8).toString('hex')
   return this.entropyToMnemonic(hex)
 }
 
diff --git a/test/index.js b/test/index.js
index 3dec071..151447e 100644
--- a/test/index.js
+++ b/test/index.js
@@ -36,12 +36,10 @@ describe('generateMnemonic', function() {
   })
 
   it('allows a custom RNG to be used', function() {
-    var rng = {
-      randomBuffer: function(size) {
-        var buffer = new Buffer(size)
-        buffer.fill(4) // guaranteed random
-        return buffer
-      }
+    var rng = function(size) {
+      var buffer = new Buffer(size)
+      buffer.fill(4) // guaranteed random
+      return buffer
     }
 
     var mnemonic = bip39.generateMnemonic(64, rng)