diff --git a/src/pretix/api/views/checkin.py b/src/pretix/api/views/checkin.py
index 8fa1290563..adddf28ec9 100644
--- a/src/pretix/api/views/checkin.py
+++ b/src/pretix/api/views/checkin.py
@@ -667,19 +667,19 @@ def _redeem_process(*, checkinlists, raw_barcode, answers_data, datetime, force,
     #    key on the same list, we're probably dealing with the ``addon_match`` case here and need to figure out
     #    which add-on has the right product.
     if len(op_candidates) > 1:
-        op_candidates_matching_product = [
-            op for op in op_candidates
-            if (
-                (list_by_event[op.order.event_id].addon_match or op.secret == raw_barcode or legacy_url_support) and
-                (list_by_event[op.order.event_id].all_products or op.item_id in {i.pk for i in list_by_event[op.order.event_id].limit_products.all()})
-            )
-        ]
-
-        if len(op_candidates_matching_product) > 1:
-            # if none of the above filters the results to 1, filter based on op.valid_from/until
-            # keep ops without valid_from/until
+        # only check addons if at most one non-addon-op is in op_candidates
+        # otherwise it is likely a medium linked to multiple orderpositions, which we need to filter based on validity
+        if len([op for op in op_candidates if not op.addon_to]) <= 1:
             op_candidates_matching_product = [
-                op for op in op_candidates_matching_product
+                op for op in op_candidates
+                if (
+                    (list_by_event[op.order.event_id].addon_match or op.secret == raw_barcode or legacy_url_support) and
+                    (list_by_event[op.order.event_id].all_products or op.item_id in {i.pk for i in list_by_event[op.order.event_id].limit_products.all()})
+                )
+            ]
+        else:
+            op_candidates_matching_product = [
+                op for op in op_candidates
                 if (
                     (not op.valid_from or op.valid_from < now()) and
                     (not op.valid_until or op.valid_until > now())
diff --git a/src/tests/api/test_checkinrpc.py b/src/tests/api/test_checkinrpc.py
index ed3169d027..ff09d36e16 100644
--- a/src/tests/api/test_checkinrpc.py
+++ b/src/tests/api/test_checkinrpc.py
@@ -310,30 +310,37 @@ def test_by_medium_multiple_orderpositions(token_client, organizer, clist, event
             organizer=organizer,
         )
         rm.linked_orderpositions.add(order.positions.first())
-        rm.linked_orderpositions.add(order.positions.all()[1])
+        op_item_other = order.positions.all()[1]
+        rm.linked_orderpositions.add(op_item_other)
+
+    # multiple tickets are valid => no check-in
     resp = _redeem(token_client, organizer, clist, "abcdef", {"source_type": "barcode"})
-    # TODO: AMBIGIOUS
-    assert resp.status_code == 201
+    assert resp.status_code == 400
+    assert resp.data['status'] == 'error'
+    assert resp.data['reason'] == 'ambiguous'
 
     with scopes_disabled():
-        op = order.positions.first()
-        op.valid_from = datetime.datetime(2020, 1, 1, 12, 0, 0, tzinfo=event.timezone)
-        op.save()
+        op_item_other.valid_from = datetime.datetime(2020, 1, 1, 12, 0, 0, tzinfo=event.timezone)
+        op_item_other.valid_until = datetime.datetime(2020, 1, 1, 15, 0, 0, tzinfo=event.timezone)
+        op_item_other.save()
 
     with freeze_time("2020-01-01 13:45:00"):
+        # multiple tickets are valid => no check-in
         resp = _redeem(token_client, organizer, clist, "abcdef", {"source_type": "barcode"})
-        # TODO: AMBIGIOUS
-        assert resp.status_code == 201 
+        assert resp.status_code == 400
+        assert resp.data['status'] == 'error'
+        assert resp.data['reason'] == 'ambiguous'
 
     with freeze_time("2020-01-01 10:45:00"):
         resp = _redeem(token_client, organizer, clist, "abcdef", {"source_type": "barcode"})
         assert resp.status_code == 201
         assert resp.data['status'] == 'ok'
 
-    with scopes_disabled():
-        ci = clist.checkins.get(position=order.positions.first())
-    assert ci.raw_barcode == "abcdef"
-    assert ci.raw_source_type == "barcode"
+    with freeze_time("2020-01-01 15:45:00"):
+        resp = _redeem(token_client, organizer, clist, "abcdef", {"source_type": "barcode"})
+        assert resp.status_code == 400
+        assert resp.data['status'] == 'error'
+        assert resp.data['reason'] == 'already_redeemed'
 
 
 @pytest.mark.django_db