diff --git a/PrivaPub.Tests/Http/OneAnswerTests.cs b/PrivaPub.Tests/Http/OneAnswerTests.cs
index 564c9d1..c5f42b2 100644
--- a/PrivaPub.Tests/Http/OneAnswerTests.cs
+++ b/PrivaPub.Tests/Http/OneAnswerTests.cs
@@ -167,6 +167,8 @@ namespace PrivaPub.Tests.Http
 			var key = group.Text("group_key");
 
 			Assert.Equal($"grouped-favourite-{id}", key);
+			// told alone (v1, a stream), each notification names the group it belongs to
+			Assert.All((await author.Client.Get("/api/v1/notifications?types[]=favourite")).Ok().Array, n => Assert.Equal(key, n.Text("group_key")));
 			Assert.Equal(2, group.Number("notifications_count"));
 			Assert.Equal(2, group["sample_account_ids"]!.AsArray().Count);
 			Assert.Equal(id, group.Text("status_id"));
diff --git a/PrivaPub/Api/Mastodon/Controllers/TimelinesController.cs b/PrivaPub/Api/Mastodon/Controllers/TimelinesController.cs
index d629e73..506f645 100644
--- a/PrivaPub/Api/Mastodon/Controllers/TimelinesController.cs
+++ b/PrivaPub/Api/Mastodon/Controllers/TimelinesController.cs
@@ -206,11 +206,11 @@ namespace PrivaPub.Api.Mastodon.Controllers
 
 		// Grouped notifications (Mastodon 4.3): api_versions.mastodon says we speak that API, so clients call it. Likes and
 		// boosts of one post group together, as do follows within an hour; everything else stands alone.
-		static readonly HashSet<string> DefaultGrouped = new() { "favourite", "reblog", "follow" };
+		internal static readonly HashSet<string> DefaultGrouped = new() { "favourite", "reblog", "follow" };
 
 		HashSet<string> Grouped() => Params.List("grouped_types") is { Count: > 0 } chosen ? chosen.ToHashSet() : DefaultGrouped;
 
-		static string GroupKey(NotificationEntity n, ISet<string> grouped) =>
+		internal static string GroupKey(NotificationEntity n, ISet<string> grouped) =>
 			!grouped.Contains(Names[n.Type]) ? $"ungrouped-{n.ID}"
 			: n.Type == NotificationType.Follow ? $"grouped-follow-{n.CreatedAt:yyyyMMddHH}"
 			: string.IsNullOrEmpty(n.PostId) ? $"ungrouped-{n.ID}"
diff --git a/PrivaPub/Api/Mastodon/Mappers/MastodonMapper.cs b/PrivaPub/Api/Mastodon/Mappers/MastodonMapper.cs
index be5ebfc..f325496 100644
--- a/PrivaPub/Api/Mastodon/Mappers/MastodonMapper.cs
+++ b/PrivaPub/Api/Mastodon/Mappers/MastodonMapper.cs
@@ -56,7 +56,8 @@ namespace PrivaPub.Api.Mastodon.Mappers
 					Id = n.ID,
 					Type = Controllers.NotificationsController.Names[n.Type],
 					CreatedAt = MastodonJson.Time(n.CreatedAt),
-					GroupKey = $"ungrouped-{n.ID}",
+					//the group it belongs to by default, so a notification told alone (v1, a stream) joins its group in a client
+					GroupKey = Controllers.NotificationsController.GroupKey(n, Controllers.NotificationsController.DefaultGrouped),
 					Account = accounts[n.FromAccountId],
 					Status = n.PostId == default ? default : statuses[n.PostId],
 					Emoji = n.Emoji == default ? default : n.EmojiURL == default ? n.Emoji : $":{n.Emoji}:",