diff --git a/swh/scheduler/backend.py b/swh/scheduler/backend.py
--- a/swh/scheduler/backend.py
+++ b/swh/scheduler/backend.py
@@ -487,6 +487,15 @@
 
         query_args.append(count)
 
+        # fmt: off
+        common_table_expressions.append(("deduplicated_selected_origins", """
+          SELECT DISTINCT
+            url, visit_type
+          FROM
+            selected_origins
+        """))
+        # fmt: on
+
         # fmt: off
         common_table_expressions.append(("update_stats", """
             INSERT INTO
@@ -494,7 +503,7 @@
             SELECT
               url, visit_type, %s
             FROM
-              selected_origins
+              deduplicated_selected_origins
             ON CONFLICT (url, visit_type) DO UPDATE
               SET last_scheduled = GREATEST(
                 origin_visit_stats.last_scheduled,
diff --git a/swh/scheduler/tests/test_scheduler.py b/swh/scheduler/tests/test_scheduler.py
--- a/swh/scheduler/tests/test_scheduler.py
+++ b/swh/scheduler/tests/test_scheduler.py
@@ -1179,6 +1179,37 @@
         with pytest.raises(UnknownPolicy, match=unknown_policy):
             swh_scheduler.grab_next_visits("type", NUM_RESULTS, policy=unknown_policy)
 
+    def test_grab_next_visit_duplicates(self, swh_scheduler, listed_origins):
+        """Checks grab_next_visits does not crash when there are rows with
+        duplicated (origin_url, visit_type) in the database
+        """
+        lister2 = swh_scheduler.get_or_create_lister(**LISTERS[1])
+        assert lister2.id != listed_origins[0].lister_id
+
+        # Create two origins with the same url and visit_type, but different listers
+        # (and also differing value for last_update so they are returned in
+        # deterministic order)
+        origin1 = attr.evolve(
+            listed_origins[0], first_seen=utcnow(), last_seen=utcnow()
+        )
+        origin2 = attr.evolve(
+            origin1,
+            lister_id=lister2.id,
+            last_update=origin1.last_update + datetime.timedelta(seconds=10),
+        )
+
+        origins = [origin1, origin2]
+        recorded_origins = swh_scheduler.record_listed_origins(origins)
+
+        expected_origins = sorted(recorded_origins, key=lambda o: o.last_update)
+
+        self._check_grab_next_visit(
+            swh_scheduler,
+            visit_type=origin1.visit_type,
+            policy="never_visited_oldest_update_first",
+            expected=expected_origins,
+        )
+
     def _create_task_types(self, scheduler):
         for tt in TASK_TYPES.values():
             scheduler.create_task_type(tt)