diff --git a/PrivaPub.Tests/Federation/GroupTests.cs b/PrivaPub.Tests/Federation/GroupTests.cs
index 5b1304f..ca46aa4 100644
--- a/PrivaPub.Tests/Federation/GroupTests.cs
+++ b/PrivaPub.Tests/Federation/GroupTests.cs
@@ -195,11 +195,13 @@ namespace PrivaPub.Tests.Federation
 			entity.Members.Add(new GroupMember { AvatarId = bob.Id });
 			await DB.Default.SaveAsync(entity, token);
 			var outsider = new RemoteActor(_harness.Peer, "asked");
-			await _harness.Remote.GetActor(outsider.Id, refresh: false, token);
+			var outsiderAccount = await _harness.Remote.GetActor(outsider.Id, refresh: false, token);
 			var asksFirst = new Post
 			{
 				ObjectURI = $"{Origin(outsider)}/notes/{Guid.NewGuid():N}",
 				ActorURI = outsider.Id,
+				GroupUserId = outsiderAccount.ID,
+				AuthorAccountId = outsiderAccount.ID,
 				IsFederatedCopy = true,
 				Visibility = PostVisibility.Public,
 				ContentHtml = "<p>ask me first</p>",
diff --git a/PrivaPub/Api/Mastodon/Mappers/MastodonMapper.cs b/PrivaPub/Api/Mastodon/Mappers/MastodonMapper.cs
index 036526d..479f76e 100644
--- a/PrivaPub/Api/Mastodon/Mappers/MastodonMapper.cs
+++ b/PrivaPub/Api/Mastodon/Mappers/MastodonMapper.cs
@@ -202,8 +202,8 @@ namespace PrivaPub.Api.Mastodon.Mappers
 
 			Status Map(PostEntity post)
 			{
-				if (!accounts.TryGetValue(AuthorOf(post), out var account))
-					return default;
+				if (AuthorOf(post) is not { } author || !accounts.TryGetValue(author, out var account))
+					return default;//a post whose author we cannot show is left out, never a 500
 				var status = new Status
 				{
 					Id = post.ID,