diff --git a/browser.js b/browser.js
index 045d523..e223c63 100644
--- a/browser.js
+++ b/browser.js
@@ -7,7 +7,7 @@
 var EC = require("elliptic").ec;
 
 var ec = new EC("secp256k1");
-var cryptoObj = window.crypto || window.msCrypto || {};
+var cryptoObj = global.crypto || global.msCrypto || {};
 var subtle = cryptoObj.subtle || cryptoObj.webkitSubtle;
 
 function assert(condition, message) {
@@ -18,7 +18,7 @@ function assert(condition, message) {
 
 function randomBytes(size) {
   var arr = new Uint8Array(size);
-  window.crypto.getRandomValues(arr);
+  global.crypto.getRandomValues(arr);
   return new Buffer(arr);
 }
 
diff --git a/index.js b/index.js
index fa0f728..017a646 100644
--- a/index.js
+++ b/index.js
@@ -9,10 +9,17 @@ var promise = typeof Promise === "undefined" ?
               require("es6-promise").Promise :
               Promise;
 var crypto = require("crypto");
-// TODO(Kagami): We may fallback to pure JS implementation
-// (`browser.js`) if this modules are failed to load.
-var secp256k1 = require("secp256k1");
-var ecdh = require("./build/Release/ecdh");
+// try to use secp256k1, fallback to browser implementation
+try {
+  var secp256k1 = require("secp256k1");
+  var ecdh = require("./build/Release/ecdh");
+} catch (e) {
+  if (process.env.ECCRYPTO_NO_FALLBACK) {
+    throw e;
+  } else {
+    return (module.exports = require("./browser"));
+  }
+}
 
 function assert(condition, message) {
   if (!condition) {
diff --git a/package.json b/package.json
index cf334f7..42117e8 100644
--- a/package.json
+++ b/package.json
@@ -6,7 +6,7 @@
   "browser": "browser.js",
   "scripts": {
     "install": "node-gyp rebuild || exit 0",
-    "test": "mocha && xvfb-run -a karma start && jshint .",
+    "test": "ECCRYPTO_NO_FALLBACK=1 mocha && xvfb-run -a karma start && jshint .",
     "m": "mocha",
     "k": "xvfb-run -a karma start",
     "kc": "xvfb-run -a karma start --browsers Chromium",