diff --git a/lib/service/activity_pub/activity_pub.ex b/lib/service/activity_pub/activity_pub.ex
index 3786f999..1636fdc6 100644
--- a/lib/service/activity_pub/activity_pub.ex
+++ b/lib/service/activity_pub/activity_pub.ex
@@ -1,3 +1,7 @@
+# Portions of this file are derived from Pleroma:
+# Copyright © 2017-2018 Pleroma Authors <https://pleroma.social>
+# SPDX-License-Identifier: AGPL-3.0-only
+
 defmodule Mobilizon.Service.ActivityPub do
   @moduledoc """
   # ActivityPub
diff --git a/lib/service/activity_pub/transmogrifier.ex b/lib/service/activity_pub/transmogrifier.ex
index 72cfd5a0..7228e7e1 100644
--- a/lib/service/activity_pub/transmogrifier.ex
+++ b/lib/service/activity_pub/transmogrifier.ex
@@ -1,3 +1,7 @@
+# Portions of this file are derived from Pleroma:
+# Copyright © 2017-2018 Pleroma Authors <https://pleroma.social>
+# SPDX-License-Identifier: AGPL-3.0-only
+
 defmodule Mobilizon.Service.ActivityPub.Transmogrifier do
   @moduledoc """
   A module to handle coding from internal to wire ActivityPub and back.
diff --git a/lib/service/activity_pub/utils.ex b/lib/service/activity_pub/utils.ex
index c878cc70..5e32c5c5 100644
--- a/lib/service/activity_pub/utils.ex
+++ b/lib/service/activity_pub/utils.ex
@@ -1,3 +1,7 @@
+# Portions of this file are derived from Pleroma:
+# Copyright © 2017-2018 Pleroma Authors <https://pleroma.social>
+# SPDX-License-Identifier: AGPL-3.0-only
+
 defmodule Mobilizon.Service.ActivityPub.Utils do
   @moduledoc """
   # Utils
diff --git a/lib/service/federator.ex b/lib/service/federator.ex
index 0711a02d..20d8c98d 100644
--- a/lib/service/federator.ex
+++ b/lib/service/federator.ex
@@ -1,3 +1,7 @@
+# Portions of this file are derived from Pleroma:
+# Copyright © 2017-2018 Pleroma Authors <https://pleroma.social>
+# SPDX-License-Identifier: AGPL-3.0-only
+
 defmodule Mobilizon.Service.Federator do
   @moduledoc """
   Handle federated activities
diff --git a/lib/service/formatter/formatter.ex b/lib/service/formatter/formatter.ex
index 77c9ca00..a13556e6 100644
--- a/lib/service/formatter/formatter.ex
+++ b/lib/service/formatter/formatter.ex
@@ -1,3 +1,7 @@
+# Portions of this file are derived from Pleroma:
+# Copyright © 2017-2018 Pleroma Authors <https://pleroma.social>
+# SPDX-License-Identifier: AGPL-3.0-only
+
 defmodule Mobilizon.Service.Formatter do
   alias Mobilizon.Actors.Actor
   alias Mobilizon.Actors
diff --git a/lib/service/http_signatures/http_signatures.ex b/lib/service/http_signatures/http_signatures.ex
index 9c1a320f..832dfd37 100644
--- a/lib/service/http_signatures/http_signatures.ex
+++ b/lib/service/http_signatures/http_signatures.ex
@@ -1,3 +1,7 @@
+# Portions of this file are derived from Pleroma:
+# Copyright © 2017-2018 Pleroma Authors <https://pleroma.social>
+# SPDX-License-Identifier: AGPL-3.0-only
+
 # https://tools.ietf.org/html/draft-cavage-http-signatures-08
 defmodule Mobilizon.Service.HTTPSignatures do
   @moduledoc """
diff --git a/lib/service/streamer.ex b/lib/service/streamer.ex
index b5665bc8..7b14ce58 100644
--- a/lib/service/streamer.ex
+++ b/lib/service/streamer.ex
@@ -1,3 +1,7 @@
+# Portions of this file are derived from Pleroma:
+# Copyright © 2017-2018 Pleroma Authors <https://pleroma.social>
+# SPDX-License-Identifier: AGPL-3.0-only
+
 defmodule Mobilizon.Service.Streamer do
   @moduledoc """
   # Streamer
diff --git a/lib/service/web_finger/web_finger.ex b/lib/service/web_finger/web_finger.ex
index dac45dba..cdaa5a99 100644
--- a/lib/service/web_finger/web_finger.ex
+++ b/lib/service/web_finger/web_finger.ex
@@ -1,3 +1,7 @@
+# Portions of this file are derived from Pleroma:
+# Copyright © 2017-2018 Pleroma Authors <https://pleroma.social>
+# SPDX-License-Identifier: AGPL-3.0-only
+
 defmodule Mobilizon.Service.WebFinger do
   @moduledoc """
   # WebFinger
diff --git a/lib/service/xml_builder.ex b/lib/service/xml_builder.ex
index 9a89d66a..c2177d54 100644
--- a/lib/service/xml_builder.ex
+++ b/lib/service/xml_builder.ex
@@ -1,3 +1,7 @@
+# Portions of this file are derived from Pleroma:
+# Copyright © 2017-2018 Pleroma Authors <https://pleroma.social>
+# SPDX-License-Identifier: AGPL-3.0-only
+
 defmodule Mobilizon.Service.XmlBuilder do
   @moduledoc """
   XML Builder.