diff --git a/redash/models.py b/redash/models.py
index 8eb346521..9d1aa06fa 100644
--- a/redash/models.py
+++ b/redash/models.py
@@ -755,7 +755,8 @@ class Alert(ModelTimestampsMixin, BaseModel):
             .join(DataSourceGroup, on=(Query.data_source==DataSourceGroup.data_source))\
             .where(DataSourceGroup.group << groups)\
             .switch(Alert)\
-            .join(User)
+            .join(User)\
+            .group_by(Alert, User, Query)
 
     @classmethod
     def get_by_id_and_org(cls, id, org):
diff --git a/tests/models/test_alerts.py b/tests/models/test_alerts.py
index 729a23b76..558ad706d 100644
--- a/tests/models/test_alerts.py
+++ b/tests/models/test_alerts.py
@@ -25,3 +25,13 @@ class TestAlertAll(BaseTestCase):
         alerts = Alert.all(groups=[group])
         self.assertNotIn(alert1, alerts)
         self.assertIn(alert2, alerts)
+
+    def test_return_each_alert_only_once(self):
+        group = self.factory.create_group()
+        self.factory.data_source.add_group(group)
+
+        alert = self.factory.create_alert()
+
+        alerts = Alert.all(groups=[self.factory.default_group, group])
+        self.assertEqual(1, len(list(alerts)))
+        self.assertIn(alert, alerts)