diff --git a/browser.js b/browser.js
index 7886210..e752ced 100644
--- a/browser.js
+++ b/browser.js
@@ -5,16 +5,17 @@
 "use strict";
 
 require("es6-promise").polyfill();
-var assert = require("assert");
 var EC = require("elliptic").ec;
 
 var ec = new EC("secp256k1");
 
 exports.getPublic = function(privateKey) {
-  // `elliptic` doesn't have such checkings so we do it ourself. We
+  // `elliptic` doesn't have such checkings so we do it by ourself. We
   // should always ensure that library user doesn't try to do something
   // dumb.
-  assert(privateKey.length === 32, "Bad private key");
+  if (privateKey.length !== 32) {
+    throw new Error("Bad private key");
+  }
   // XXX(Kagami): `elliptic.utils.encode` returns array for every
   // encoding except `hex`.
   return new Buffer(ec.keyPair(privateKey).getPublic("arr"));