diff --git a/ormar/models/mixins/save_mixin.py b/ormar/models/mixins/save_mixin.py
index 52826b7..5ff29ad 100644
--- a/ormar/models/mixins/save_mixin.py
+++ b/ormar/models/mixins/save_mixin.py
@@ -224,7 +224,7 @@ class SavePrepareMixin(RelationMixin, AliasMixin):
     async def _upsert_through_model(
         instance: "Model",
         previous_model: "Model",
-        relation_field: Optional["ForeignKeyField"],
+        relation_field: "ForeignKeyField",
     ) -> None:
         """
         Upsert through model for m2m relation.