diff --git a/mongoengine/base.py b/mongoengine/base.py
index 0cbd707..1f7ba1f 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 65b397d..8fcb1d6 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
 import gridfs
diff --git a/mongoengine/queryset.py b/mongoengine/queryset.py
index 48936e6..9941785 100644
--- a/mongoengine/queryset.py
+++ b/mongoengine/queryset.py
@@ -2,6 +2,9 @@ from connection import _get_db
 
 import pprint
 import pymongo
+import pymongo.code
+import pymongo.dbref
+import pymongo.objectid
 import re
 import copy