diff --git a/lib/delta.js b/lib/delta.js
index cd52128..b36a50e 100644
--- a/lib/delta.js
+++ b/lib/delta.js
@@ -23,7 +23,7 @@ Delta.prototype.insert = function (text, attributes) {
   var newOp = {};
   if (text.length === 0) return this;
   newOp.insert = text;
-  if (typeof attributes === 'object' && Object.keys(attributes).length > 0) newOp.attributes = attributes;
+  if (attributes instanceof Object && Object.keys(attributes).length > 0) newOp.attributes = attributes;
   return this.push(newOp);
 };
 
@@ -35,7 +35,7 @@ Delta.prototype['delete'] = function (length) {
 Delta.prototype.retain = function (length, attributes) {
   if (length <= 0) return this;
   var newOp = { retain: length };
-  if (typeof attributes === 'object' && Object.keys(attributes).length > 0) newOp.attributes = attributes;
+  if (attributes instanceof Object && Object.keys(attributes).length > 0) newOp.attributes = attributes;
   return this.push(newOp);
 };
 
diff --git a/test/delta/builder.js b/test/delta/builder.js
index d922fef..d956211 100644
--- a/test/delta/builder.js
+++ b/test/delta/builder.js
@@ -49,6 +49,12 @@ describe('insert()', function () {
     expect(delta.ops[0]).toEqual({ insert: 'test' });
   });
 
+  it('insert(text, null)', function () {
+    var delta = new Delta().insert('test', null);
+    expect(delta.ops.length).toEqual(1);
+    expect(delta.ops[0]).toEqual({ insert: 'test' });
+  });
+
   it('insert(embed)', function () {
     var delta = new Delta().insert(1);
     expect(delta.ops.length).toEqual(1);
@@ -132,6 +138,12 @@ describe('retain()', function () {
     expect(delta.ops[0]).toEqual({ retain: 2 });
   });
 
+  it('retain(length, null)', function () {
+    var delta = new Delta().retain(2, null);
+    expect(delta.ops.length).toEqual(1);
+    expect(delta.ops[0]).toEqual({ retain: 2 });
+  });
+
   it('retain(length, attributes)', function () {
     var delta = new Delta().retain(1, { bold: true });
     expect(delta.ops.length).toEqual(1);