diff --git a/model_clone/mixin.py b/model_clone/mixin.py
index d8b39625..181fecc1 100644
--- a/model_clone/mixin.py
+++ b/model_clone/mixin.py
@@ -532,6 +532,8 @@ def __duplicate_m2o_fields(self, duplicate, using=None):
                             item_clone = item.make_clone(using=using)
                         except IntegrityError:
                             item_clone = item.make_clone(sub_clone=True)
+                    elif item is None:
+                        item_clone = None
                     else:
                         item.pk = None  # pragma: no cover
                         item_clone = item.save(using=using)  # pragma: no cover