diff --git a/lib/stringify.js b/lib/stringify.js
index 0b21ca75..12a96e65 100644
--- a/lib/stringify.js
+++ b/lib/stringify.js
@@ -133,7 +133,7 @@ module.exports = function (object, opts) {
     var obj = object;
     var options = opts ? utils.assign({}, opts) : {};
 
-    if (options.encoder !== null && options.encoder !== undefined && typeof options.encoder !== 'function') {
+    if (options.encoder !== null && typeof options.encoder !== 'undefined' && typeof options.encoder !== 'function') {
         throw new TypeError('Encoder has to be a function.');
     }