diff --git a/docs/changelog.rst b/docs/changelog.rst
index 3569132d..8199e03e 100644
--- a/docs/changelog.rst
+++ b/docs/changelog.rst
@@ -4,6 +4,7 @@ Changelog
 
 Changes in 0.8.4
 ================
+- Update transform to handle docs erroneously passed to unset (#416)
 - Fixed indexing - turn off _cls (#414)
 - Fixed dereference threading issue in ComplexField.__get__ (#412)
 - Fixed QuerySetNoCache.count() caching (#410)
diff --git a/mongoengine/queryset/transform.py b/mongoengine/queryset/transform.py
index 352774ff..e0a7d3c6 100644
--- a/mongoengine/queryset/transform.py
+++ b/mongoengine/queryset/transform.py
@@ -203,11 +203,13 @@ def update(_doc_cls=None, **update):
                     value = field.prepare_query_value(op, value)
             elif op in ('pushAll', 'pullAll'):
                 value = [field.prepare_query_value(op, v) for v in value]
-            elif op == 'addToSet':
+            elif op in ('addToSet', 'setOnInsert'):
                 if isinstance(value, (list, tuple, set)):
                     value = [field.prepare_query_value(op, v) for v in value]
                 elif field.required or value is not None:
                     value = field.prepare_query_value(op, value)
+            elif op == "unset":
+                value = 1
 
         if match:
             match = '$' + match
diff --git a/tests/queryset/transform.py b/tests/queryset/transform.py
index 7886965b..d2e8b784 100644
--- a/tests/queryset/transform.py
+++ b/tests/queryset/transform.py
@@ -31,6 +31,31 @@ class TransformTest(unittest.TestCase):
         self.assertEqual(transform.query(name__exists=True),
                          {'name': {'$exists': True}})
 
+    def test_transform_update(self):
+        class DicDoc(Document):
+            dictField = DictField()
+
+        class Doc(Document):
+            pass
+
+        DicDoc.drop_collection()
+        Doc.drop_collection()
+
+        doc = Doc().save()
+        dic_doc = DicDoc().save()
+
+        for k, v in (("set", "$set"), ("set_on_insert", "$setOnInsert"), ("push", "$push")):
+            update = transform.update(DicDoc, **{"%s__dictField__test" % k: doc})
+            self.assertTrue(isinstance(update[v]["dictField.test"], dict))
+
+        # Update special cases
+        update = transform.update(DicDoc, unset__dictField__test=doc)
+        self.assertEqual(update["$unset"]["dictField.test"], 1)
+
+        update = transform.update(DicDoc, pull__dictField__test=doc)
+        self.assertTrue(isinstance(update["$pull"]["dictField"]["test"], dict))
+
+
     def test_query_field_name(self):
         """Ensure that the correct field name is used when querying.
         """