diff --git a/CHANGELOG.md b/CHANGELOG.md
index 7fe3bf687..0c5e43123 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 ### Security
 - OStatus: eliminate the possibility of a protocol downgrade attack.
 - OStatus: prevent following locked accounts, bypassing the approval process.
+- Mastodon API: respect post privacy in `/api/v1/statuses/:id/{favourited,reblogged}_by`
 
 ### Removed
 - **Breaking:** GNU Social API with Qvitter extensions support
diff --git a/lib/pleroma/user.ex b/lib/pleroma/user.ex
index 5e10ac25f..64b69e686 100644
--- a/lib/pleroma/user.ex
+++ b/lib/pleroma/user.ex
@@ -174,11 +174,25 @@ def following_count(%User{} = user) do
     |> Repo.aggregate(:count, :id)
   end
 
+  defp truncate_if_exists(params, key, max_length) do
+    if Map.has_key?(params, key) and is_binary(params[key]) do
+      {value, _chopped} = String.split_at(params[key], max_length)
+      Map.put(params, key, value)
+    else
+      params
+    end
+  end
+
   def remote_user_creation(params) do
     bio_limit = Pleroma.Config.get([:instance, :user_bio_length], 5000)
     name_limit = Pleroma.Config.get([:instance, :user_name_length], 100)
 
-    params = Map.put(params, :info, params[:info] || %{})
+    params =
+      params
+      |> Map.put(:info, params[:info] || %{})
+      |> truncate_if_exists(:name, name_limit)
+      |> truncate_if_exists(:bio, bio_limit)
+
     info_cng = User.Info.remote_user_creation(%User.Info{}, params[:info])
 
     changes =
diff --git a/lib/pleroma/user/info.ex b/lib/pleroma/user/info.ex
index 779bfbc18..151e025de 100644
--- a/lib/pleroma/user/info.ex
+++ b/lib/pleroma/user/info.ex
@@ -242,6 +242,13 @@ def set_keys(info, keys) do
   end
 
   def remote_user_creation(info, params) do
+    params =
+      if Map.has_key?(params, :fields) do
+        Map.put(params, :fields, Enum.map(params[:fields], &truncate_field/1))
+      else
+        params
+      end
+
     info
     |> cast(params, [
       :ap_enabled,
@@ -326,6 +333,16 @@ defp valid_field?(%{"name" => name, "value" => value}) do
 
   defp valid_field?(_), do: false
 
+  defp truncate_field(%{"name" => name, "value" => value}) do
+    {name, _chopped} =
+      String.split_at(name, Pleroma.Config.get([:instance, :account_field_name_length], 255))
+
+    {value, _chopped} =
+      String.split_at(value, Pleroma.Config.get([:instance, :account_field_value_length], 255))
+
+    %{"name" => name, "value" => value}
+  end
+
   @spec confirmation_changeset(Info.t(), keyword()) :: Changeset.t()
   def confirmation_changeset(info, opts) do
     need_confirmation? = Keyword.get(opts, :need_confirmation)
diff --git a/lib/pleroma/web/mastodon_api/controllers/mastodon_api_controller.ex b/lib/pleroma/web/mastodon_api/controllers/mastodon_api_controller.ex
index 0940e07a6..060137b80 100644
--- a/lib/pleroma/web/mastodon_api/controllers/mastodon_api_controller.ex
+++ b/lib/pleroma/web/mastodon_api/controllers/mastodon_api_controller.ex
@@ -842,6 +842,7 @@ def get_mascot(%{assigns: %{user: user}} = conn, _params) do
 
   def favourited_by(%{assigns: %{user: user}} = conn, %{"id" => id}) do
     with %Activity{} = activity <- Activity.get_by_id_with_object(id),
+         {:visible, true} <- {:visible, Visibility.visible_for_user?(activity, user)},
          %Object{data: %{"likes" => likes}} <- Object.normalize(activity) do
       q = from(u in User, where: u.ap_id in ^likes)
 
@@ -853,12 +854,14 @@ def favourited_by(%{assigns: %{user: user}} = conn, %{"id" => id}) do
       |> put_view(AccountView)
       |> render("accounts.json", %{for: user, users: users, as: :user})
     else
+      {:visible, false} -> {:error, :not_found}
       _ -> json(conn, [])
     end
   end
 
   def reblogged_by(%{assigns: %{user: user}} = conn, %{"id" => id}) do
     with %Activity{} = activity <- Activity.get_by_id_with_object(id),
+         {:visible, true} <- {:visible, Visibility.visible_for_user?(activity, user)},
          %Object{data: %{"announcements" => announces}} <- Object.normalize(activity) do
       q = from(u in User, where: u.ap_id in ^announces)
 
@@ -870,6 +873,7 @@ def reblogged_by(%{assigns: %{user: user}} = conn, %{"id" => id}) do
       |> put_view(AccountView)
       |> render("accounts.json", %{for: user, users: users, as: :user})
     else
+      {:visible, false} -> {:error, :not_found}
       _ -> json(conn, [])
     end
   end
diff --git a/test/activity_test.exs b/test/activity_test.exs
index f9f789a76..275cab81e 100644
--- a/test/activity_test.exs
+++ b/test/activity_test.exs
@@ -213,7 +213,11 @@ test "all_by_actor_and_id/2" do
 
     assert [] == Activity.all_by_actor_and_id(user, [])
 
-    assert [%Activity{id: ^id2}, %Activity{id: ^id1}] =
-             Activity.all_by_actor_and_id(user.ap_id, [id1, id2])
+    activities =
+      user.ap_id
+      |> Activity.all_by_actor_and_id([id1, id2])
+      |> Enum.sort(&(&1.id < &2.id))
+
+    assert [%Activity{id: ^id1}, %Activity{id: ^id2}] = activities
   end
 end
diff --git a/test/user_test.exs b/test/user_test.exs
index 05b158025..4d79f858a 100644
--- a/test/user_test.exs
+++ b/test/user_test.exs
@@ -570,22 +570,6 @@ test "it has required fields" do
         refute cs.valid?
       end)
     end
-
-    test "it restricts some sizes" do
-      bio_limit = Pleroma.Config.get([:instance, :user_bio_length], 5000)
-      name_limit = Pleroma.Config.get([:instance, :user_name_length], 100)
-
-      [bio: bio_limit, name: name_limit]
-      |> Enum.each(fn {field, size} ->
-        string = String.pad_leading(".", size)
-        cs = User.remote_user_creation(Map.put(@valid_remote, field, string))
-        assert cs.valid?
-
-        string = String.pad_leading(".", size + 1)
-        cs = User.remote_user_creation(Map.put(@valid_remote, field, string))
-        refute cs.valid?
-      end)
-    end
   end
 
   describe "followers and friends" do
@@ -1117,11 +1101,60 @@ test "get_public_key_for_ap_id fetches a user that's not in the db" do
     assert {:ok, _key} = User.get_public_key_for_ap_id("http://mastodon.example.org/users/admin")
   end
 
-  test "insert or update a user from given data" do
-    user = insert(:user, %{nickname: "nick@name.de"})
-    data = %{ap_id: user.ap_id <> "xxx", name: user.name, nickname: user.nickname}
+  describe "insert or update a user from given data" do
+    test "with normal data" do
+      user = insert(:user, %{nickname: "nick@name.de"})
+      data = %{ap_id: user.ap_id <> "xxx", name: user.name, nickname: user.nickname}
 
-    assert {:ok, %User{}} = User.insert_or_update_user(data)
+      assert {:ok, %User{}} = User.insert_or_update_user(data)
+    end
+
+    test "with overly long fields" do
+      current_max_length = Pleroma.Config.get([:instance, :account_field_value_length], 255)
+      user = insert(:user, nickname: "nickname@supergood.domain")
+
+      data = %{
+        ap_id: user.ap_id,
+        name: user.name,
+        nickname: user.nickname,
+        info: %{
+          fields: [
+            %{"name" => "myfield", "value" => String.duplicate("h", current_max_length + 1)}
+          ]
+        }
+      }
+
+      assert {:ok, %User{}} = User.insert_or_update_user(data)
+    end
+
+    test "with an overly long bio" do
+      current_max_length = Pleroma.Config.get([:instance, :user_bio_length], 5000)
+      user = insert(:user, nickname: "nickname@supergood.domain")
+
+      data = %{
+        ap_id: user.ap_id,
+        name: user.name,
+        nickname: user.nickname,
+        bio: String.duplicate("h", current_max_length + 1),
+        info: %{}
+      }
+
+      assert {:ok, %User{}} = User.insert_or_update_user(data)
+    end
+
+    test "with an overly long display name" do
+      current_max_length = Pleroma.Config.get([:instance, :user_name_length], 100)
+      user = insert(:user, nickname: "nickname@supergood.domain")
+
+      data = %{
+        ap_id: user.ap_id,
+        name: String.duplicate("h", current_max_length + 1),
+        nickname: user.nickname,
+        info: %{}
+      }
+
+      assert {:ok, %User{}} = User.insert_or_update_user(data)
+    end
   end
 
   describe "per-user rich-text filtering" do
diff --git a/test/web/mastodon_api/mastodon_api_controller_test.exs b/test/web/mastodon_api/mastodon_api_controller_test.exs
index 806ae7e69..061c3a8ad 100644
--- a/test/web/mastodon_api/mastodon_api_controller_test.exs
+++ b/test/web/mastodon_api/mastodon_api_controller_test.exs
@@ -3698,7 +3698,7 @@ test "returns 404 when poll is private and not available for user", %{conn: conn
         build_conn()
         |> assign(:user, user)
 
-      [conn: conn, activity: activity]
+      [conn: conn, activity: activity, user: user]
     end
 
     test "returns users who have favorited the status", %{conn: conn, activity: activity} do
@@ -3758,6 +3758,32 @@ test "does not fail on an unauthenticated request", %{conn: conn, activity: acti
       [%{"id" => id}] = response
       assert id == other_user.id
     end
+
+    test "requires authentification for private posts", %{conn: conn, user: user} do
+      other_user = insert(:user)
+
+      {:ok, activity} =
+        CommonAPI.post(user, %{
+          "status" => "@#{other_user.nickname} wanna get some #cofe together?",
+          "visibility" => "direct"
+        })
+
+      {:ok, _, _} = CommonAPI.favorite(activity.id, other_user)
+
+      conn
+      |> assign(:user, nil)
+      |> get("/api/v1/statuses/#{activity.id}/favourited_by")
+      |> json_response(404)
+
+      response =
+        build_conn()
+        |> assign(:user, other_user)
+        |> get("/api/v1/statuses/#{activity.id}/favourited_by")
+        |> json_response(200)
+
+      [%{"id" => id}] = response
+      assert id == other_user.id
+    end
   end
 
   describe "GET /api/v1/statuses/:id/reblogged_by" do
@@ -3769,7 +3795,7 @@ test "does not fail on an unauthenticated request", %{conn: conn, activity: acti
         build_conn()
         |> assign(:user, user)
 
-      [conn: conn, activity: activity]
+      [conn: conn, activity: activity, user: user]
     end
 
     test "returns users who have reblogged the status", %{conn: conn, activity: activity} do
@@ -3829,6 +3855,29 @@ test "does not fail on an unauthenticated request", %{conn: conn, activity: acti
       [%{"id" => id}] = response
       assert id == other_user.id
     end
+
+    test "requires authentification for private posts", %{conn: conn, user: user} do
+      other_user = insert(:user)
+
+      {:ok, activity} =
+        CommonAPI.post(user, %{
+          "status" => "@#{other_user.nickname} wanna get some #cofe together?",
+          "visibility" => "direct"
+        })
+
+      conn
+      |> assign(:user, nil)
+      |> get("/api/v1/statuses/#{activity.id}/reblogged_by")
+      |> json_response(404)
+
+      response =
+        build_conn()
+        |> assign(:user, other_user)
+        |> get("/api/v1/statuses/#{activity.id}/reblogged_by")
+        |> json_response(200)
+
+      assert [] == response
+    end
   end
 
   describe "POST /auth/password, with valid parameters" do