diff --git a/src/Squidex.Domain.Apps.Entities/Apps/Guards/GuardAppContributors.cs b/src/Squidex.Domain.Apps.Entities/Apps/Guards/GuardAppContributors.cs
index 23b0bd390..e7411d8bb 100644
--- a/src/Squidex.Domain.Apps.Entities/Apps/Guards/GuardAppContributors.cs
+++ b/src/Squidex.Domain.Apps.Entities/Apps/Guards/GuardAppContributors.cs
@@ -45,7 +45,7 @@ namespace Squidex.Domain.Apps.Entities.Apps.Guards
                     {
                         command.ContributorId = user.Id;
 
-                        if (string.Equals(command.ContributorId, command.Actor.Identifier, StringComparison.OrdinalIgnoreCase))
+                        if (string.Equals(command.ContributorId, command.Actor?.Identifier, StringComparison.OrdinalIgnoreCase))
                         {
                             error(new ValidationError("You cannot change your own permission."));
                         }