diff --git a/mongoengine/fields.py b/mongoengine/fields.py
index 127f029f..73bc7562 100644
--- a/mongoengine/fields.py
+++ b/mongoengine/fields.py
@@ -319,8 +319,8 @@ class ListField(BaseField):
 
     def prepare_query_value(self, op, value):
         if op in ('set', 'unset'):
-            return [self.field.to_mongo(v) for v in value]
-        return self.field.to_mongo(value)
+            return [self.field.prepare_query_value(op, v) for v in value]
+        return self.field.prepare_query_value(op, value)
 
     def lookup_member(self, member_name):
         return self.field.lookup_member(member_name)