diff --git a/lib/pleroma/web/mastodon_api/mastodon_api_controller.ex b/lib/pleroma/web/mastodon_api/mastodon_api_controller.ex
index e03027be7..f6cf081fd 100644
--- a/lib/pleroma/web/mastodon_api/mastodon_api_controller.ex
+++ b/lib/pleroma/web/mastodon_api/mastodon_api_controller.ex
@@ -508,6 +508,7 @@ defmodule Pleroma.Web.MastodonAPI.MastodonAPIController do
       |> Map.put("type", "Create")
       |> Map.put("local_only", local_only)
       |> Map.put("blocking_user", user)
+      |> Map.put("tag", String.downcase(params["tag"]))
 
     activities =
       ActivityPub.fetch_public_activities(params)