diff --git a/doc/api/resources/checkinlists.rst b/doc/api/resources/checkinlists.rst
index 07664f60c..bbd34612b 100644
--- a/doc/api/resources/checkinlists.rst
+++ b/doc/api/resources/checkinlists.rst
@@ -611,8 +611,12 @@ Order position endpoints
    Tries to redeem an order position, identified by its internal ID, i.e. checks the attendee in. This endpoint
    accepts a number of optional requests in the body.
 
-   **Tip:** Instead of an ID, you can also use the ``secret`` field as the lookup parameter.
+   **Tip:** Instead of an ID, you can also use the ``secret`` field as the lookup parameter. In this case, you should
+   always set ``untrusted_input=true`` as a query parameter to avoid security issues.
 
+   :query boolean untrusted_input: If set to true, the lookup parameter is **always** interpreted as a ``secret``, never
+                                   as an ``id``. This should be always set if you are passing through untrusted, scanned
+                                   data to avoid guessing of ticket IDs.
    :<json boolean questions_supported: When this parameter is set to ``true``, handling of questions is supported. If
                                        you do not implement question handling in your user interface, you **must**
                                        set this to ``false``. In that case, questions will just be ignored. Defaults
diff --git a/src/pretix/api/views/checkin.py b/src/pretix/api/views/checkin.py
index bf32a6340..c6c2dffe6 100644
--- a/src/pretix/api/views/checkin.py
+++ b/src/pretix/api/views/checkin.py
@@ -409,6 +409,11 @@ class CheckinListPositionViewSet(viewsets.ReadOnlyModelViewSet):
         ignore_unpaid = bool(self.request.data.get('ignore_unpaid', False))
         nonce = self.request.data.get('nonce')
 
+        untrusted_input = (
+            self.request.GET.get('untrusted_input', '') not in ('0', 'false', 'False', '')
+            or (isinstance(self.request.auth, Device) and 'pretixscan' in (self.request.auth.software_brand or '').lower())
+        )
+
         if 'datetime' in self.request.data:
             dt = DateTimeField().to_internal_value(self.request.data.get('datetime'))
         else:
@@ -429,7 +434,7 @@ class CheckinListPositionViewSet(viewsets.ReadOnlyModelViewSet):
 
         try:
             queryset = self.get_queryset(ignore_status=True, ignore_products=True)
-            if self.kwargs['pk'].isnumeric():
+            if self.kwargs['pk'].isnumeric() and not untrusted_input:
                 op = queryset.get(Q(pk=self.kwargs['pk']) | Q(secret=self.kwargs['pk']))
             else:
                 # In application/x-www-form-urlencoded, you can encodes space ' ' with '+' instead of '%20'.
diff --git a/src/pretix/plugins/webcheckin/static/pretixplugins/webcheckin/components/app.vue b/src/pretix/plugins/webcheckin/static/pretixplugins/webcheckin/components/app.vue
index c6af56038..a2994c7a4 100644
--- a/src/pretix/plugins/webcheckin/static/pretixplugins/webcheckin/components/app.vue
+++ b/src/pretix/plugins/webcheckin/static/pretixplugins/webcheckin/components/app.vue
@@ -128,7 +128,7 @@
             </p>
           </div>
           <div class="modal-footer">
-            <button type="button" class="btn btn-primary pull-right" @click="check(checkResult.position.secret, true, false, false)">
+            <button type="button" class="btn btn-primary pull-right" @click="check(checkResult.position.secret, true, false, false, true)">
               {{ $root.strings['modal.continue'] }}
             </button>
             <button type="button" class="btn btn-default" @click="showUnpaidModal = false">
@@ -188,7 +188,7 @@
             </div>
           </div>
           <div class="modal-footer">
-            <button type="button" class="btn btn-primary pull-right" @click="check(checkResult.position.secret, true, true)">
+            <button type="button" class="btn btn-primary pull-right" @click="check(checkResult.position.secret, true, true, true)">
               {{ $root.strings['modal.continue'] }}
             </button>
             <button type="button" class="btn btn-default" @click="showQuestionsModal = false">
@@ -296,7 +296,7 @@ export default {
   },
   methods: {
     selectResult(res) {
-      this.check(res.id, false, false, false)
+      this.check(res.id, false, false, false, false)
     },
     answerSetM(qid, opid, checked) {
       let arr = this.answers[qid] ? this.answers[qid].split(',') : [];
@@ -320,7 +320,7 @@ export default {
       this.showQuestionsModal = false
       this.answers = {}
     },
-    check(id, ignoreUnpaid, keepAnswers, fallbackToSearch) {
+    check(id, ignoreUnpaid, keepAnswers, fallbackToSearch, untrusted) {
       if (!keepAnswers) {
         this.answers = {}
       } else if (this.showQuestionsModal) {
@@ -339,7 +339,11 @@ export default {
         this.$refs.input.blur()
       })
 
-      fetch(this.$root.api.lists + this.checkinlist.id + '/positions/' + encodeURIComponent(id) + '/redeem/?expand=item&expand=subevent&expand=variation', {
+      let url = this.$root.api.lists + this.checkinlist.id + '/positions/' + encodeURIComponent(id) + '/redeem/?expand=item&expand=subevent&expand=variation'
+      if (untrusted)  {
+        url += '&untrusted_input=true'
+      }
+      fetch(url, {
         method: 'POST',
         headers: {
           'X-CSRFToken': document.querySelector("input[name=csrfmiddlewaretoken]").value,
@@ -439,7 +443,7 @@ export default {
     startSearch(fallbackToScan) {
       if (this.query.length >= 32 && fallbackToScan) {
         // likely a secret, not a search result
-        this.check(this.query, false, false, true)
+        this.check(this.query, false, false, true, true)
         return
       }
 
diff --git a/src/tests/api/test_checkin.py b/src/tests/api/test_checkin.py
index 09a5ccf49..18ee2bb1c 100644
--- a/src/tests/api/test_checkin.py
+++ b/src/tests/api/test_checkin.py
@@ -1199,7 +1199,6 @@ def test_redeem_unknown_legacy_device_bug(device, device_client, organizer, clis
     ), {
         'force': True
     }, format='json')
-    print(resp.data)
     assert resp.status_code == 400
     assert resp.data["status"] == "error"
     assert resp.data["reason"] == "already_redeemed"
@@ -1219,3 +1218,43 @@ def test_redeem_unknown_legacy_device_bug(device, device_client, organizer, clis
     assert resp.data["reason"] == "invalid"
     with scopes_disabled():
         assert not Checkin.objects.last()
+
+
+@pytest.mark.django_db
+def test_redeem_by_id_not_allowed_if_pretixscan(device, device_client, organizer, clist, event, order):
+    with scopes_disabled():
+        p = order.positions.first()
+    device.software_brand = "pretixSCAN"
+    device.software_version = "1.14.2"
+    device.save()
+    resp = device_client.post('/api/v1/organizers/{}/events/{}/checkinlists/{}/positions/{}/redeem/'.format(
+        organizer.slug, event.slug, clist.pk, p.pk
+    ), {
+        'force': True
+    }, format='json')
+    print(resp.data)
+    assert resp.status_code == 404
+    resp = device_client.post('/api/v1/organizers/{}/events/{}/checkinlists/{}/positions/{}/redeem/'.format(
+        organizer.slug, event.slug, clist.pk, p.secret
+    ), {
+        'force': True
+    }, format='json')
+    assert resp.status_code == 201
+
+
+@pytest.mark.django_db
+def test_redeem_by_id_not_allowed_if_untrusted(device, device_client, organizer, clist, event, order):
+    with scopes_disabled():
+        p = order.positions.first()
+    resp = device_client.post('/api/v1/organizers/{}/events/{}/checkinlists/{}/positions/{}/redeem/?untrusted_input=true'.format(
+        organizer.slug, event.slug, clist.pk, p.pk
+    ), {
+        'force': True
+    }, format='json')
+    assert resp.status_code == 404
+    resp = device_client.post('/api/v1/organizers/{}/events/{}/checkinlists/{}/positions/{}/redeem/?untrusted_input=true'.format(
+        organizer.slug, event.slug, clist.pk, p.secret
+    ), {
+        'force': True
+    }, format='json')
+    assert resp.status_code == 201