diff --git a/taiga/projects/notifications/mixins.py b/taiga/projects/notifications/mixins.py
index e6e6fc74..bf42a9ed 100644
--- a/taiga/projects/notifications/mixins.py
+++ b/taiga/projects/notifications/mixins.py
@@ -191,7 +191,11 @@ class WatchedResourceModelSerializer(serializers.ModelSerializer):
         watcher_field = self.fields.pop("watchers", None)
         instance = super(WatchedResourceModelSerializer, self).restore_object(attrs, instance)
         if instance is not None and self.validate_watchers(attrs, "watchers"):
-            new_watcher_ids = set(attrs.get("watchers", []))
+            #A partial update can exclude the watchers field
+            if not "watchers" in attrs:
+                return instance
+
+            new_watcher_ids = set(attrs.get("watchers", None))
             old_watcher_ids = set(instance.get_watchers().values_list("id", flat=True))
             adding_watcher_ids = list(new_watcher_ids.difference(old_watcher_ids))
             removing_watcher_ids = list(old_watcher_ids.difference(new_watcher_ids))
@@ -209,7 +213,6 @@ class WatchedResourceModelSerializer(serializers.ModelSerializer):
 
         return instance
 
-
     def to_native(self, obj):
         #watchers is wasn't attached via the get_queryset of the viewset we need to manually add it
         if obj is not None and not hasattr(obj, "watchers"):
@@ -217,6 +220,12 @@ class WatchedResourceModelSerializer(serializers.ModelSerializer):
 
         return super(WatchedResourceModelSerializer, self).to_native(obj)
 
+    def save(self, **kwargs):
+        obj = super(WatchedResourceModelSerializer, self).save(**kwargs)
+        self.fields["watchers"] = WatchersField(required=False)
+        obj.watchers = [user.id for user in obj.get_watchers()]
+        return obj
+
 
 class WatchersViewSetMixin:
     # Is a ModelListViewSet with two required params: permission_classes and resource_model
diff --git a/tests/integration/test_userstories.py b/tests/integration/test_userstories.py
index 33b18a8d..f90fd97a 100644
--- a/tests/integration/test_userstories.py
+++ b/tests/integration/test_userstories.py
@@ -443,3 +443,21 @@ def test_custom_fields_csv_generation():
     assert row[26] == attr.name
     row = next(reader)
     assert row[26] == "val1"
+
+
+def test_update_userstory_respecting_watchers(client):
+    watching_user = f.create_user()
+    project = f.ProjectFactory.create()
+    us = f.UserStoryFactory.create(project=project, status__project=project, milestone__project=project)
+    us.add_watcher(watching_user)
+    f.MembershipFactory.create(project=us.project, user=us.owner, is_owner=True)
+    f.MembershipFactory.create(project=us.project, user=watching_user)
+
+    client.login(user=us.owner)
+    url = reverse("userstories-detail", kwargs={"pk": us.pk})
+    data = {"subject": "Updating test", "version": 1}
+
+    response = client.json.patch(url, json.dumps(data))
+    assert response.status_code == 200
+    assert response.data["subject"] == "Updating test"
+    assert response.data["watchers"] == [watching_user.id]