diff --git a/lib/rng-browser.js b/lib/rng-browser.js
index 6361fb81..dead6ada 100644
--- a/lib/rng-browser.js
+++ b/lib/rng-browser.js
@@ -23,12 +23,16 @@ if (getRandomValues) {
   // quality.
   var rnds = new Array(16);
 
-  module.exports = function mathRNG() {
+  function mathRNG() {
     for (var i = 0, r; i < 16; i++) {
       if ((i & 0x03) === 0) r = Math.random() * 0x100000000;
       rnds[i] = r >>> ((i & 0x03) << 3) & 0xff;
     }
 
     return rnds;
-  };
+  }
+  mathRNG.insecure = true;
+  mathRNG.insecureMessage = 'No CSPRNG provided. Provide a cryptographically secure rng' +
+                          ' via `rng` option or set `allowInsecureRNG` to true';
+  module.exports = mathRNG;
 }
diff --git a/test/test.js b/test/test.js
index d15df3e7..1a48881b 100644
--- a/test/test.js
+++ b/test/test.js
@@ -64,6 +64,8 @@ test('mathRNG', function() {
   var rng = require('../lib/rng-browser');
   assert.equal(rng.name, 'mathRNG');
 
+  assert.equal(rng.insecure, true)
+
   var bytes = rng();
   assert.equal(bytes.length, 16);
 
diff --git a/v1.js b/v1.js
index d84c0f45..745a33f7 100644
--- a/v1.js
+++ b/v1.js
@@ -22,6 +22,9 @@ function v1(options, buf, offset) {
   var node = options.node || _nodeId;
   var clockseq = options.clockseq !== undefined ? options.clockseq : _clockseq;
 
+  if (rng.insecure && !options.allowInsecureRNG)
+    throw new Error(rng.insecureMessage);
+
   // node and clockseq need to be initialized to random values if they're not
   // specified.  We do this lazily to minimize issues related to insufficient
   // system entropy.  See #189
diff --git a/v4.js b/v4.js
index 1f07be1c..893a2f0e 100644
--- a/v4.js
+++ b/v4.js
@@ -12,6 +12,9 @@ function v4(options, buf, offset) {
 
   var rnds = options.random || (options.rng || rng)();
 
+  if (rng.insecure && !options.allowInsecureRNG)
+    throw new Error(rng.insecureMessage);
+
   // Per 4.4, set bits for version and `clock_seq_hi_and_reserved`
   rnds[6] = (rnds[6] & 0x0f) | 0x40;
   rnds[8] = (rnds[8] & 0x3f) | 0x80;