diff --git a/lib/async.js b/lib/async.js
index 29962c3..3af2c49 100644
--- a/lib/async.js
+++ b/lib/async.js
@@ -93,7 +93,7 @@ module.exports = function (password, salt, iterations, keylen, digest, callback)
   var algo = toBrowser[digest.toLowerCase()]
 
   if (!algo || typeof global.Promise !== 'function') {
-    return getNextTick()(function () {
+    getNextTick()(function () {
       var out
       try {
         out = sync(password, salt, iterations, keylen, digest)
@@ -102,6 +102,7 @@ module.exports = function (password, salt, iterations, keylen, digest, callback)
       }
       callback(null, out)
     })
+    return
   }
 
   checkParameters(iterations, keylen)