diff --git a/zds/tutorialv2/tests/tests_utils.py b/zds/tutorialv2/tests/tests_utils.py
index 4e52de2902..c3bcc62e2d 100644
--- a/zds/tutorialv2/tests/tests_utils.py
+++ b/zds/tutorialv2/tests/tests_utils.py
@@ -556,7 +556,7 @@ def test_no_alert_on_unpublish(self):
         reaction = ContentReactionFactory(
             related_content=published, author=ProfileFactory().user, position=1, pubdate=datetime.datetime.now()
         )
-        Alert.objects.create(
+        alert = Alert.objects.create(
             scope="CONTENT",
             comment=reaction,
             text="a text",
@@ -569,6 +569,15 @@ def test_no_alert_on_unpublish(self):
         unpublish_content(published, staff)
         self.assertEqual(0, get_header_notifications(staff)["alerts"]["total"])
 
+        # Try to solve the alert anyway (related to #6478):
+        self.client.force_login(self.staff)
+        result = self.client.post(
+            reverse("content:resolve-content", kwargs={"pk": published.pk}),
+            {"alert_pk": alert.pk, "text": "Anéfé!"},
+            follow=False,
+        )
+        self.assertEqual(result.status_code, 404)
+
     def tearDown(self):
         super().tearDown()
         PublicatorRegistry.registry = self.old_registry
diff --git a/zds/tutorialv2/views/alerts.py b/zds/tutorialv2/views/alerts.py
index d120707b1e..880e592bfa 100644
--- a/zds/tutorialv2/views/alerts.py
+++ b/zds/tutorialv2/views/alerts.py
@@ -62,6 +62,9 @@ def post(self, request, *args, **kwargs):
         except (KeyError, ValueError):
             raise Http404("L'alerte n'existe pas.")
 
+        if alert.solved:
+            raise Http404("L'alerte a déjà été résolue.")
+
         resolve_reason = ""
         msg_title = ""
         msg_content = ""