lib/pleroma/web/mastodon_api/views/status_view.ex

@@ -424,13 +424,12 @@ def render("history.json", %{activity: %{data: %{"object" => _object}} = activit
       |> Enum.map(&Map.put(&1, "id", object.data["id"]))
       |> Enum.map(&%Object{data: &1, id: object.id})
 
-    history = [object | past_history]
-
-    history_len = length(history)
-
     history =
-      Enum.zip(history_len..0, history)
-      |> Enum.map(fn {chrono_order, object} ->
+      [object | past_history]
+      # Mastodon expects the original to be at the first
+      |> Enum.reverse()
+      |> Enum.with_index()
+      |> Enum.map(fn {object, chrono_order} ->
         %{
           # The history is prepended every time there is a new edit.
           # In chrono_order, the oldest item is always at 0, and so on.

test/pleroma/web/mastodon_api/controllers/status_controller_test.exs

@@ -2084,7 +2084,7 @@ test "edited post", %{conn: conn} do
 
       conn = get(conn, "/api/v1/statuses/#{activity.id}/history")
 
-      assert [_, %{"spoiler_text" => "title 2"}, %{"spoiler_text" => "title 1"}] =
+      assert [%{"spoiler_text" => "title 1"}, %{"spoiler_text" => "title 2"}, _] =
                json_response_and_validate_schema(conn, 200)
     end
   end