diff --git a/contentcuration/contentcuration/tests/viewsets/test_invitation.py b/contentcuration/contentcuration/tests/viewsets/test_invitation.py
index f044f50a99..e5eed46387 100644
--- a/contentcuration/contentcuration/tests/viewsets/test_invitation.py
+++ b/contentcuration/contentcuration/tests/viewsets/test_invitation.py
@@ -446,3 +446,77 @@ def test_update_invitation_decline(self):
             ).exists()
         )
         self.assertTrue(models.Change.objects.filter(channel=self.channel).exists())
+
+    def test_accept_invitation_by_channel_editor_is_forbidden(self):
+        invitation = models.Invitation.objects.create(**self.invitation_db_metadata)
+
+        self.client.force_authenticate(user=self.user)
+        response = self.client.post(
+            reverse("invitation-accept", kwargs={"pk": invitation.id})
+        )
+        self.assertEqual(response.status_code, 403, response.content)
+        invitation.refresh_from_db()
+        self.assertFalse(invitation.accepted)
+
+    def test_decline_invitation_by_channel_editor_is_forbidden(self):
+        invitation = models.Invitation.objects.create(**self.invitation_db_metadata)
+
+        self.client.force_authenticate(user=self.user)
+        response = self.client.post(
+            reverse("invitation-decline", kwargs={"pk": invitation.id})
+        )
+        self.assertEqual(response.status_code, 403, response.content)
+        invitation.refresh_from_db()
+        self.assertFalse(invitation.declined)
+
+    def test_accept_invitation_by_unrelated_user_is_not_found(self):
+        invitation = models.Invitation.objects.create(**self.invitation_db_metadata)
+        unrelated_user = testdata.user("unrelated@example.com")
+
+        self.client.force_authenticate(user=unrelated_user)
+        response = self.client.post(
+            reverse("invitation-accept", kwargs={"pk": invitation.id})
+        )
+        self.assertEqual(response.status_code, 404, response.content)
+        invitation.refresh_from_db()
+        self.assertFalse(invitation.accepted)
+
+    def test_decline_invitation_by_unrelated_user_is_not_found(self):
+        invitation = models.Invitation.objects.create(**self.invitation_db_metadata)
+        unrelated_user = testdata.user("unrelated@example.com")
+
+        self.client.force_authenticate(user=unrelated_user)
+        response = self.client.post(
+            reverse("invitation-decline", kwargs={"pk": invitation.id})
+        )
+        self.assertEqual(response.status_code, 404, response.content)
+        invitation.refresh_from_db()
+        self.assertFalse(invitation.declined)
+
+    def test_accept_invitation_by_admin_succeeds(self):
+        invitation = models.Invitation.objects.create(**self.invitation_db_metadata)
+        admin_user = testdata.user("admin@example.com")
+        admin_user.is_admin = True
+        admin_user.save()
+
+        self.client.force_authenticate(user=admin_user)
+        response = self.client.post(
+            reverse("invitation-accept", kwargs={"pk": invitation.id})
+        )
+        self.assertEqual(response.status_code, 200, response.content)
+        invitation.refresh_from_db()
+        self.assertTrue(invitation.accepted)
+
+    def test_decline_invitation_by_admin_succeeds(self):
+        invitation = models.Invitation.objects.create(**self.invitation_db_metadata)
+        admin_user = testdata.user("admin@example.com")
+        admin_user.is_admin = True
+        admin_user.save()
+
+        self.client.force_authenticate(user=admin_user)
+        response = self.client.post(
+            reverse("invitation-decline", kwargs={"pk": invitation.id})
+        )
+        self.assertEqual(response.status_code, 200, response.content)
+        invitation.refresh_from_db()
+        self.assertTrue(invitation.declined)
diff --git a/contentcuration/contentcuration/viewsets/invitation.py b/contentcuration/contentcuration/viewsets/invitation.py
index 7d8ff577f6..cd500cd74c 100644
--- a/contentcuration/contentcuration/viewsets/invitation.py
+++ b/contentcuration/contentcuration/viewsets/invitation.py
@@ -2,6 +2,7 @@
 from django_filters.rest_framework import FilterSet
 from rest_framework import serializers
 from rest_framework.decorators import action
+from rest_framework.exceptions import PermissionDenied
 from rest_framework.permissions import IsAuthenticated
 from rest_framework.response import Response
 
@@ -137,9 +138,16 @@ def perform_update(self, serializer):
         instance = serializer.save()
         instance.save()
 
+    def _ensure_invitee(self, request, invitation):
+        if request.user.is_admin:
+            return
+        if (request.user.email or "").lower() != (invitation.email or "").lower():
+            raise PermissionDenied("Only the invited user may perform this action.")
+
     @action(detail=True, methods=["post"])
     def accept(self, request, pk=None):
-        invitation = self.get_object()
+        invitation = self.get_edit_object()
+        self._ensure_invitee(request, invitation)
         invitation.accept()
         invitation.accepted = True
         invitation.save()
@@ -157,7 +165,8 @@ def accept(self, request, pk=None):
 
     @action(detail=True, methods=["post"])
     def decline(self, request, pk=None):
-        invitation = self.get_object()
+        invitation = self.get_edit_object()
+        self._ensure_invitee(request, invitation)
         invitation.declined = True
         invitation.save()
         Change.create_change(