diff --git a/lib/web/controllers/activity_pub_controller.ex b/lib/web/controllers/activity_pub_controller.ex
index 93f13282..2d97e4a5 100644
--- a/lib/web/controllers/activity_pub_controller.ex
+++ b/lib/web/controllers/activity_pub_controller.ex
@@ -85,8 +85,9 @@ defmodule Mobilizon.Web.ActivityPubController do
         actor = Map.get(conn.assigns, :actor)
 
         if actor_applicant_group_member?(group, actor) do
-          json(
-            conn,
+          conn
+          |> put_resp_content_type("application/activity+json")
+          |> json(
             ActorView.render("member.json", %{
               member: member,
               actor_applicant: actor
@@ -168,7 +169,7 @@ defmodule Mobilizon.Web.ActivityPubController do
   def relay(conn, _params) do
     with {status, %Actor{} = actor} when status in [:commit, :ok] <- Cache.get_relay() do
       conn
-      |> put_resp_header("content-type", "application/activity+json")
+      |> put_resp_content_type("application/activity+json")
       |> json(ActorView.render("actor.json", %{actor: actor}))
     end
   end
@@ -194,7 +195,7 @@ defmodule Mobilizon.Web.ActivityPubController do
          page <- max(page, 1),
          %Actor{} = actor <- Actors.get_local_actor_by_name_with_preload(name) do
       conn
-      |> put_resp_header("content-type", "application/activity+json")
+      |> put_resp_content_type("application/activity+json")
       |> json(
         ActorView.render("#{collection}.json", %{
           actor: actor,
@@ -208,7 +209,7 @@ defmodule Mobilizon.Web.ActivityPubController do
   defp actor_collection(conn, collection, %{"name" => name}) do
     with %Actor{} = actor <- Actors.get_local_actor_by_name_with_preload(name) do
       conn
-      |> put_resp_header("content-type", "application/activity+json")
+      |> put_resp_content_type("application/activity+json")
       |> json(
         ActorView.render("#{collection}.json", %{
           actor: actor,
diff --git a/lib/web/controllers/page_controller.ex b/lib/web/controllers/page_controller.ex
index cc00560a..9afb1f77 100644
--- a/lib/web/controllers/page_controller.ex
+++ b/lib/web/controllers/page_controller.ex
@@ -141,11 +141,13 @@ defmodule Mobilizon.Web.PageController do
           %Tombstone{} ->
             conn
             |> put_status(:gone)
+            |> maybe_add_content_type_header()
             |> render(object_type, object: object)
 
           _ ->
             conn
             |> maybe_add_noindex_header(object)
+            |> maybe_add_content_type_header()
             |> render(object_type, object: object)
         end
 
@@ -199,4 +201,14 @@ defmodule Mobilizon.Web.PageController do
   @spec is_person?(Actor.t()) :: boolean()
   defp is_person?(%Actor{type: :Person}), do: true
   defp is_person?(_), do: false
+
+  defp maybe_add_content_type_header(conn) do
+    case get_format(conn) do
+      "html" ->
+        conn
+
+      "activity-json" ->
+        put_resp_content_type(conn, "application/activity+json")
+    end
+  end
 end