diff --git a/mongoengine/fields.py b/mongoengine/fields.py
index 13fa6689..beb8ae00 100644
--- a/mongoengine/fields.py
+++ b/mongoengine/fields.py
@@ -209,20 +209,19 @@ class ReferenceField(BaseField):
         return super(ReferenceField, self).__get__(instance, owner)
 
     def to_mongo(self, document):
-        if isinstance(document, (str, unicode, pymongo.objectid.ObjectId)):
-            # document may already be an object id
-            id_ = document
-        else:
+        id_field_name = self.document_type._meta['id_field']
+        id_field = self.document_type._fields[id_field_name]
+
+        if isinstance(document, Document):
             # We need the id from the saved object to create the DBRef
             id_ = document.id
             if id_ is None:
                 raise ValidationError('You can only reference documents once '
                                       'they have been saved to the database')
+        else:
+            id_ = document
 
-        # id may be a string rather than an ObjectID object
-        if not isinstance(id_, pymongo.objectid.ObjectId):
-            id_ = pymongo.objectid.ObjectId(id_)
-
+        id_ = id_field.to_mongo(id_)
         collection = self.document_type._meta['collection']
         return pymongo.dbref.DBRef(collection, id_)
     
diff --git a/tests/fields.py b/tests/fields.py
index affb0c9b..0ebb143d 100644
--- a/tests/fields.py
+++ b/tests/fields.py
@@ -259,6 +259,40 @@ class FieldTest(unittest.TestCase):
         User.drop_collection()
         BlogPost.drop_collection()
 
+    def test_reference_query_conversion(self):
+        """Ensure that ReferenceFields can be queried using objects and values
+        of the type of the primary key of the referenced object.
+        """
+        class Member(Document):
+            user_num = IntField(primary_key=True)
+
+        class BlogPost(Document):
+            title = StringField()
+            author = ReferenceField(Member)
+
+        Member.drop_collection()
+        BlogPost.drop_collection()
+
+        m1 = Member(user_num=1)
+        m1.save()
+        m2 = Member(user_num=2)
+        m2.save()
+
+        post1 = BlogPost(title='post 1', author=m1)
+        post1.save()
+
+        post2 = BlogPost(title='post 2', author=m2)
+        post2.save()
+
+        post = BlogPost.objects(author=m1.id).first()
+        self.assertEqual(post.id, post1.id)
+
+        post = BlogPost.objects(author=m2.id).first()
+        self.assertEqual(post.id, post2.id)
+
+        Member.drop_collection()
+        BlogPost.drop_collection()
+
 
 if __name__ == '__main__':
     unittest.main()