diff --git a/mongoengine/base.py b/mongoengine/base.py
index c8c162b..22347a2 100644
--- a/mongoengine/base.py
+++ b/mongoengine/base.py
@@ -3,6 +3,7 @@ from queryset import DoesNotExist, MultipleObjectsReturned
 
 import sys
 import pymongo
+import pymongo.objectid
 
 
 _document_registry = {}
diff --git a/mongoengine/fields.py b/mongoengine/fields.py
index 127f029..7883f78 100644
--- a/mongoengine/fields.py
+++ b/mongoengine/fields.py
@@ -5,6 +5,9 @@ from operator import itemgetter
 
 import re
 import pymongo
+import pymongo.dbref
+import pymongo.son
+import pymongo.binary
 import datetime
 import decimal
 
diff --git a/mongoengine/queryset.py b/mongoengine/queryset.py
index 069ab11..faf0cf4 100644
--- a/mongoengine/queryset.py
+++ b/mongoengine/queryset.py
@@ -1,6 +1,9 @@
 from connection import _get_db
 
 import pymongo
+import pymongo.code
+import pymongo.dbref
+import pymongo.objectid
 import re
 import copy