diff --git a/lib/crypto/pbkdf2-browser.js b/lib/crypto/pbkdf2-browser.js
index 9ecd1849..5366bed8 100644
--- a/lib/crypto/pbkdf2-browser.js
+++ b/lib/crypto/pbkdf2-browser.js
@@ -13,7 +13,7 @@
 
 var digest = require('./digest');
 var crypto = global.crypto || global.msCrypto || {};
-var subtle = crypto.subtle && crypto.subtle.importKey ? crypto.subtle : {};
+var subtle = crypto.subtle || {};
 
 /**
  * Perform key derivation using PBKDF2.
@@ -62,32 +62,27 @@ exports.derive = function derive(key, salt, iter, len, alg) {
  * @returns {Promise}
  */
 
-exports.deriveAsync = function deriveAsync(key, salt, iter, len, alg) {
+exports.deriveAsync = async function deriveAsync(key, salt, iter, len, alg) {
   var algo = { name: 'PBKDF2' };
   var use = ['deriveBits'];
-  var name = getHash(alg);
-  var length = len * 8;
-  var options, promise;
+  var options, key, data;
+
+  if (!subtle.importKey || !subtle.deriveBits)
+    return exports.derive(key, salt, iter, len, alg);
 
   options = {
     name: 'PBKDF2',
     salt: salt,
     iterations: iter,
-    hash: name
+    hash: getHash(alg)
   };
 
-  promise = subtle.importKey('raw', key, algo, false, use);
+  key = await subtle.importKey('raw', key, algo, false, use);
+  data = await subtle.deriveBits(options, key, len * 8);
 
-  return promise.then(function(key) {
-    return subtle.deriveBits(options, key, length);
-  }).then(function(result) {
-    return Buffer.from(result);
-  });
+  return Buffer.from(data);
 };
 
-if (!subtle.deriveBits)
-  exports.pbkdf2Async = exports.pbkdf2;
-
 /*
  * Helpers
  */
diff --git a/lib/crypto/pbkdf2.js b/lib/crypto/pbkdf2.js
index ac37b170..f246d8f5 100644
--- a/lib/crypto/pbkdf2.js
+++ b/lib/crypto/pbkdf2.js
@@ -10,8 +10,8 @@
  * @module crypto.pbkdf2
  */
 
-var co = require('../utils/co');
 var crypto = require('crypto');
+var co = require('../utils/co');
 
 /**
  * Perform key derivation using PBKDF2.