diff --git a/src/documents/serialisers.py b/src/documents/serialisers.py
index 94504fcd0..648052797 100644
--- a/src/documents/serialisers.py
+++ b/src/documents/serialisers.py
@@ -1247,30 +1247,31 @@ class DocumentSerializer(
 
             validated_data["tags"] = list(final_tags)
         if validated_data.get("remove_inbox_tags"):
-            tag_ids_being_added = (
-                [
-                    tag.id
-                    for tag in validated_data["tags"]
-                    if tag not in instance.tags.all()
-                ]
+            current_tag_ids = {t.pk for t in instance.tags.all()}
+            tags = (
+                validated_data["tags"]
                 if "tags" in validated_data
-                else []
+                else list(instance.tags.all())
             )
-            inbox_tags_not_being_added = Tag.objects.filter(is_inbox_tag=True).exclude(
-                id__in=tag_ids_being_added,
-            )
-            if "tags" in validated_data:
-                validated_data["tags"] = [
-                    tag
-                    for tag in validated_data["tags"]
-                    if tag not in inbox_tags_not_being_added
-                ]
-            else:
-                validated_data["tags"] = [
-                    tag
-                    for tag in instance.tags.all()
-                    if tag not in inbox_tags_not_being_added
-                ]
+
+            # Tags newly added in this update, plus their ancestors, are kept
+            keep_ids: set[int] = set()
+            for tag in tags:
+                if tag.pk not in current_tag_ids:
+                    keep_ids.add(tag.pk)
+                    keep_ids.update(int(pk) for pk in tag.get_ancestors_pks())
+
+            # Remove inbox tags and their descendants, except those being kept
+            remove_ids: set[int] = set()
+            for inbox_tag in (
+                Tag.objects.filter(is_inbox_tag=True)
+                .exclude(pk__in=keep_ids)
+                .only("pk", "tn_descendants_pks")
+            ):
+                remove_ids.add(inbox_tag.pk)
+                remove_ids.update(int(pk) for pk in inbox_tag.get_descendants_pks())
+
+            validated_data["tags"] = [t for t in tags if t.pk not in remove_ids]
 
         if settings.AUDIT_LOG_ENABLED:
             with set_actor(self.user):
diff --git a/src/documents/tests/test_tag_hierarchy.py b/src/documents/tests/test_tag_hierarchy.py
index b439d5d70..ed0bff351 100644
--- a/src/documents/tests/test_tag_hierarchy.py
+++ b/src/documents/tests/test_tag_hierarchy.py
@@ -2,6 +2,7 @@ from unittest import mock
 
 from django.contrib.auth.models import Permission
 from django.contrib.auth.models import User
+from rest_framework import status
 from rest_framework.test import APITestCase
 
 from documents import bulk_edit
@@ -108,6 +109,44 @@ class TestTagHierarchy(DirectoriesMixin, APITestCase):
         self.document.refresh_from_db()
         assert self.document.tags.count() == 0
 
+    def test_remove_inbox_tags_removes_nested_children(self) -> None:
+        inbox = Tag.objects.create(name="Inbox", is_inbox_tag=True)
+        nested = Tag.objects.create(name="Nested", tn_parent=inbox)
+        self.document.add_nested_tags([nested])
+
+        resp = self.client.patch(
+            f"/api/documents/{self.document.pk}/",
+            {"title": "new title", "remove_inbox_tags": True},
+            format="json",
+        )
+        assert resp.status_code == status.HTTP_200_OK
+        self.document.refresh_from_db()
+        assert self.document.tags.count() == 0
+
+        # A subsequent save must not re-add the inbox tag as an ancestor
+        resp = self.client.patch(
+            f"/api/documents/{self.document.pk}/",
+            {"title": "another title", "tags": [], "remove_inbox_tags": True},
+            format="json",
+        )
+        assert resp.status_code == status.HTTP_200_OK
+        self.document.refresh_from_db()
+        assert self.document.tags.count() == 0
+
+    def test_remove_inbox_tags_keeps_inbox_when_nested_child_added(self) -> None:
+        inbox = Tag.objects.create(name="Inbox", is_inbox_tag=True)
+        nested = Tag.objects.create(name="Nested", tn_parent=inbox)
+        self.document.add_nested_tags([inbox])
+
+        self.client.patch(
+            f"/api/documents/{self.document.pk}/",
+            {"tags": [nested.pk], "remove_inbox_tags": True},
+            format="json",
+        )
+        self.document.refresh_from_db()
+        tags = set(self.document.tags.values_list("pk", flat=True))
+        assert tags == {inbox.pk, nested.pk}
+
     def test_bulk_edit_respects_hierarchy(self) -> None:
         bulk_edit.add_tag([self.document.pk], self.child.pk)
         self.document.refresh_from_db()