diff --git a/lib/pleroma/web/activity_pub/activity_pub.ex b/lib/pleroma/web/activity_pub/activity_pub.ex
index 8086c830c..bb54c885c 100644
--- a/lib/pleroma/web/activity_pub/activity_pub.ex
+++ b/lib/pleroma/web/activity_pub/activity_pub.ex
@@ -144,6 +144,24 @@ defmodule Pleroma.Web.ActivityPub.ActivityPub do
     end
   end
 
+  def unannounce(
+        %User{} = actor,
+        %Object{} = object,
+        activity_id \\ nil,
+        local \\ true
+      ) do
+    with %Activity{} = announce_activity <- get_existing_announce(actor.ap_id, object),
+         unannounce_data <- make_unannounce_data(actor, announce_activity, activity_id),
+         {:ok, unannounce_activity} <- insert(unannounce_data, local),
+         :ok <- maybe_federate(unannounce_activity),
+         {:ok, _activity} <- Repo.delete(announce_activity),
+         {:ok, object} <- remove_announce_from_object(announce_activity, object) do
+      {:ok, unannounce_activity, announce_activity, object}
+    else
+      _e -> {:ok, object}
+    end
+  end
+
   def follow(follower, followed, activity_id \\ nil, local \\ true) do
     with data <- make_follow_data(follower, followed, activity_id),
          {:ok, activity} <- insert(data, local),
diff --git a/lib/pleroma/web/activity_pub/transmogrifier.ex b/lib/pleroma/web/activity_pub/transmogrifier.ex
index 5f86f67cd..463d1e59d 100644
--- a/lib/pleroma/web/activity_pub/transmogrifier.ex
+++ b/lib/pleroma/web/activity_pub/transmogrifier.ex
@@ -223,9 +223,27 @@ defmodule Pleroma.Web.ActivityPub.Transmogrifier do
     end
   end
 
+  def handle_incoming(
+        %{
+          "type" => "Undo",
+          "object" => %{"type" => "Announce", "object" => object_id},
+          "actor" => actor,
+          "id" => id
+        } = data
+      ) do
+    with %User{} = actor <- User.get_or_fetch_by_ap_id(actor),
+         {:ok, object} <-
+           get_obj_helper(object_id) || ActivityPub.fetch_object_from_id(object_id),
+         {:ok, activity, _, _} <- ActivityPub.unannounce(actor, object, id, false) do
+      {:ok, activity}
+    else
+      e -> :error
+    end
+  end
+
   # TODO
   # Accept
-  # Undo
+  # Undo for non-Announce
 
   def handle_incoming(_), do: :error
 
diff --git a/lib/pleroma/web/activity_pub/utils.ex b/lib/pleroma/web/activity_pub/utils.ex
index 7b2bf8fa7..f98545336 100644
--- a/lib/pleroma/web/activity_pub/utils.ex
+++ b/lib/pleroma/web/activity_pub/utils.ex
@@ -238,6 +238,28 @@ defmodule Pleroma.Web.ActivityPub.Utils do
   #### Announce-related helpers
 
   @doc """
+  Retruns an existing announce activity if the notice has already been announced
+  """
+  def get_existing_announce(actor, %{data: %{"id" => id}}) do
+    query =
+      from(
+        activity in Activity,
+        where: fragment("(?)->>'actor' = ?", activity.data, ^actor),
+        # this is to use the index
+        where:
+          fragment(
+            "coalesce((?)->'object'->>'id', (?)->>'object') = ?",
+            activity.data,
+            activity.data,
+            ^id
+          ),
+        where: fragment("(?)->>'type' = 'Announce'", activity.data)
+      )
+
+    Repo.one(query)
+  end
+
+  @doc """
   Make announce activity data for the given actor and object
   """
   def make_announce_data(
@@ -257,12 +279,38 @@ defmodule Pleroma.Web.ActivityPub.Utils do
     if activity_id, do: Map.put(data, "id", activity_id), else: data
   end
 
+  @doc """
+  Make unannounce activity data for the given actor and object
+  """
+  def make_unannounce_data(
+        %User{ap_id: ap_id} = user,
+        %Activity{data: %{"context" => context}} = activity,
+        activity_id
+      ) do
+    data = %{
+      "type" => "Undo",
+      "actor" => ap_id,
+      "object" => activity.data,
+      "to" => [user.follower_address, activity.data["actor"]],
+      "cc" => ["https://www.w3.org/ns/activitystreams#Public"],
+      "context" => context
+    }
+
+    if activity_id, do: Map.put(data, "id", activity_id), else: data
+  end
+
   def add_announce_to_object(%Activity{data: %{"actor" => actor}}, object) do
     with announcements <- [actor | object.data["announcements"] || []] |> Enum.uniq() do
       update_element_in_object("announcement", announcements, object)
     end
   end
 
+  def remove_announce_from_object(%Activity{data: %{"actor" => actor}}, object) do
+    with announcements <- (object.data["announcements"] || []) |> List.delete(actor) do
+      update_element_in_object("announcement", announcements, object)
+    end
+  end
+
   #### Unfollow-related helpers
 
   def make_unfollow_data(follower, followed, follow_activity) do
diff --git a/lib/pleroma/web/common_api/common_api.ex b/lib/pleroma/web/common_api/common_api.ex
index 14a68929d..8845419c2 100644
--- a/lib/pleroma/web/common_api/common_api.ex
+++ b/lib/pleroma/web/common_api/common_api.ex
@@ -24,6 +24,16 @@ defmodule Pleroma.Web.CommonAPI do
     end
   end
 
+  def unrepeat(id_or_ap_id, user) do
+    with %Activity{} = activity <- get_by_id_or_ap_id(id_or_ap_id),
+         object <- Object.get_by_ap_id(activity.data["object"]["id"]) do
+      ActivityPub.unannounce(user, object)
+    else
+      _ ->
+        {:error, "Could not unrepeat"}
+    end
+  end
+
   def favorite(id_or_ap_id, user) do
     with %Activity{} = activity <- get_by_id_or_ap_id(id_or_ap_id),
          false <- activity.data["actor"] == user.ap_id,
diff --git a/lib/pleroma/web/mastodon_api/mastodon_api_controller.ex b/lib/pleroma/web/mastodon_api/mastodon_api_controller.ex
index 9f4261143..5475cb505 100644
--- a/lib/pleroma/web/mastodon_api/mastodon_api_controller.ex
+++ b/lib/pleroma/web/mastodon_api/mastodon_api_controller.ex
@@ -308,6 +308,13 @@ defmodule Pleroma.Web.MastodonAPI.MastodonAPIController do
     end
   end
 
+  def unreblog_status(%{assigns: %{user: user}} = conn, %{"id" => ap_id_or_id}) do
+    with {:ok, _, _, %{data: %{"id" => id}}} = CommonAPI.unrepeat(ap_id_or_id, user),
+         %Activity{} = activity <- Activity.get_create_activity_by_object_ap_id(id) do
+      render(conn, StatusView, "status.json", %{activity: activity, for: user, as: :activity})
+    end
+  end
+
   def fav_status(%{assigns: %{user: user}} = conn, %{"id" => ap_id_or_id}) do
     with {:ok, _fav, %{data: %{"id" => id}}} = CommonAPI.favorite(ap_id_or_id, user),
          %Activity{} = activity <- Activity.get_create_activity_by_object_ap_id(id) do
diff --git a/lib/pleroma/web/ostatus/activity_representer.ex b/lib/pleroma/web/ostatus/activity_representer.ex
index e8841a856..64cadba1b 100644
--- a/lib/pleroma/web/ostatus/activity_representer.ex
+++ b/lib/pleroma/web/ostatus/activity_representer.ex
@@ -239,27 +239,35 @@ defmodule Pleroma.Web.OStatus.ActivityRepresenter do
     inserted_at = activity.data["published"]
 
     author = if with_author, do: [{:author, UserRepresenter.to_simple_form(user)}], else: []
-    follow_activity = Activity.get_by_ap_id(activity.data["object"])
+
+    follow_activity =
+      if is_map(activity.data["object"]) do
+        Activity.get_by_ap_id(activity.data["object"]["id"])
+      else
+        Activity.get_by_ap_id(activity.data["object"])
+      end
 
     mentions = (activity.recipients || []) |> get_mentions
 
-    [
-      {:"activity:object-type", ['http://activitystrea.ms/schema/1.0/activity']},
-      {:"activity:verb", ['http://activitystrea.ms/schema/1.0/unfollow']},
-      {:id, h.(activity.data["id"])},
-      {:title, ['#{user.nickname} stopped following #{follow_activity.data["object"]}']},
-      {:content, [type: 'html'],
-       ['#{user.nickname} stopped following #{follow_activity.data["object"]}']},
-      {:published, h.(inserted_at)},
-      {:updated, h.(updated_at)},
-      {:"activity:object",
-       [
-         {:"activity:object-type", ['http://activitystrea.ms/schema/1.0/person']},
-         {:id, h.(follow_activity.data["object"])},
-         {:uri, h.(follow_activity.data["object"])}
-       ]},
-      {:link, [rel: 'self', type: ['application/atom+xml'], href: h.(activity.data["id"])], []}
-    ] ++ mentions ++ author
+    if follow_activity do
+      [
+        {:"activity:object-type", ['http://activitystrea.ms/schema/1.0/activity']},
+        {:"activity:verb", ['http://activitystrea.ms/schema/1.0/unfollow']},
+        {:id, h.(activity.data["id"])},
+        {:title, ['#{user.nickname} stopped following #{follow_activity.data["object"]}']},
+        {:content, [type: 'html'],
+         ['#{user.nickname} stopped following #{follow_activity.data["object"]}']},
+        {:published, h.(inserted_at)},
+        {:updated, h.(updated_at)},
+        {:"activity:object",
+         [
+           {:"activity:object-type", ['http://activitystrea.ms/schema/1.0/person']},
+           {:id, h.(follow_activity.data["object"])},
+           {:uri, h.(follow_activity.data["object"])}
+         ]},
+        {:link, [rel: 'self', type: ['application/atom+xml'], href: h.(activity.data["id"])], []}
+      ] ++ mentions ++ author
+    end
   end
 
   def to_simple_form(%{data: %{"type" => "Delete"}} = activity, user, with_author) do
diff --git a/lib/pleroma/web/router.ex b/lib/pleroma/web/router.ex
index c025dea33..c202cb810 100644
--- a/lib/pleroma/web/router.ex
+++ b/lib/pleroma/web/router.ex
@@ -112,6 +112,7 @@ defmodule Pleroma.Web.Router do
     delete("/statuses/:id", MastodonAPIController, :delete_status)
 
     post("/statuses/:id/reblog", MastodonAPIController, :reblog_status)
+    post("/statuses/:id/unreblog", MastodonAPIController, :unreblog_status)
     post("/statuses/:id/favourite", MastodonAPIController, :fav_status)
     post("/statuses/:id/unfavourite", MastodonAPIController, :unfav_status)
 
diff --git a/lib/pleroma/web/salmon/salmon.ex b/lib/pleroma/web/salmon/salmon.ex
index 10542fd00..562ec3d9c 100644
--- a/lib/pleroma/web/salmon/salmon.ex
+++ b/lib/pleroma/web/salmon/salmon.ex
@@ -187,13 +187,14 @@ defmodule Pleroma.Web.Salmon do
 
   def publish(%{info: %{"keys" => keys}} = user, %{data: %{"type" => type}} = activity, poster)
       when type in @supported_activities do
-    feed =
-      ActivityRepresenter.to_simple_form(activity, user, true)
-      |> ActivityRepresenter.wrap_with_entry()
-      |> :xmerl.export_simple(:xmerl_xml)
-      |> to_string
+    feed = ActivityRepresenter.to_simple_form(activity, user, true)
 
     if feed do
+      feed =
+        ActivityRepresenter.wrap_with_entry(feed)
+        |> :xmerl.export_simple(:xmerl_xml)
+        |> to_string
+
       {:ok, private, _} = keys_from_pem(keys)
       {:ok, feed} = encode(private, feed)
 
diff --git a/lib/pleroma/web/twitter_api/twitter_api.ex b/lib/pleroma/web/twitter_api/twitter_api.ex
index 44ea40a4e..8177a4988 100644
--- a/lib/pleroma/web/twitter_api/twitter_api.ex
+++ b/lib/pleroma/web/twitter_api/twitter_api.ex
@@ -11,6 +11,18 @@ defmodule Pleroma.Web.TwitterAPI.TwitterAPI do
     CommonAPI.post(user, data)
   end
 
+  def delete(%User{} = user, id) do
+    # TwitterAPI does not have an "unretweet" endpoint; instead this is done
+    # via the "destroy" endpoint.  Therefore, we need to handle
+    # when the status to "delete" is actually an Announce (repeat) object.
+    with %Activity{data: %{"type" => type}} <- Repo.get(Activity, id) do
+      case type do
+        "Announce" -> unrepeat(user, id)
+        _ -> CommonAPI.delete(id, user)
+      end
+    end
+  end
+
   def follow(%User{} = follower, params) do
     with {:ok, %User{} = followed} <- get_user(params),
          {:ok, follower} <- User.follow(follower, followed),
@@ -63,6 +75,12 @@ defmodule Pleroma.Web.TwitterAPI.TwitterAPI do
     end
   end
 
+  defp unrepeat(%User{} = user, ap_id_or_id) do
+    with {:ok, _unannounce, activity, _object} <- CommonAPI.unrepeat(ap_id_or_id, user) do
+      {:ok, activity}
+    end
+  end
+
   def fav(%User{} = user, ap_id_or_id) do
     with {:ok, _announce, %{data: %{"id" => id}}} = CommonAPI.favorite(ap_id_or_id, user),
          %Activity{} = activity <- Activity.get_create_activity_by_object_ap_id(id) do
diff --git a/lib/pleroma/web/twitter_api/twitter_api_controller.ex b/lib/pleroma/web/twitter_api/twitter_api_controller.ex
index 960925f42..a99487738 100644
--- a/lib/pleroma/web/twitter_api/twitter_api_controller.ex
+++ b/lib/pleroma/web/twitter_api/twitter_api_controller.ex
@@ -157,8 +157,8 @@ defmodule Pleroma.Web.TwitterAPI.Controller do
   end
 
   def delete_post(%{assigns: %{user: user}} = conn, %{"id" => id}) do
-    with {:ok, delete} <- CommonAPI.delete(id, user) do
-      render(conn, ActivityView, "activity.json", %{activity: delete, for: user})
+    with {:ok, activity} <- TwitterAPI.delete(user, id) do
+      render(conn, ActivityView, "activity.json", %{activity: activity, for: user})
     end
   end
 
diff --git a/test/fixtures/mastodon-undo-announce.json b/test/fixtures/mastodon-undo-announce.json
new file mode 100644
index 000000000..05332bed2
--- /dev/null
+++ b/test/fixtures/mastodon-undo-announce.json
@@ -0,0 +1,47 @@
+{
+   "type": "Undo",
+   "signature": {
+     "type": "RsaSignature2017",
+     "signatureValue": "VU9AmHf3Pus9cWtMG/TOdxr+MRQfPHdTVKBBgFJBXhAlMhxEtcbxsu7zmqBgfIz6u0HpTCi5jRXEMftc228OJf/aBUkr4hyWADgcdmhPQgpibouDLgQf9BmnrPqb2rMbzZyt49GJkQZma8taLh077TTq6OKcnsAAJ1evEKOcRYS4OxBSwh4nI726bOXzZWoNzpTcrnm+llcUEN980sDSAS0uyZdb8AxZdfdG6DJQX4AkUD5qTpfqP/vC1ISirrNphvVhlxjUV9Amr4SYTsLx80vdZe5NjeL5Ir4jTIIQLedpxaDu1M9Q+Jpc0fYByQ2hOwUq8JxEmvHvarKjrq0Oww==",
+     "creator": "http://mastodon.example.org/users/admin#main-key",
+     "created": "2018-05-11T16:23:45Z"
+   },
+   "object": {
+     "type": "Announce",
+     "to": [
+       "http://www.w3.org/ns/activitystreams#Public"
+     ],
+     "published": "2018-05-11T16:23:37Z",
+     "object": "http://mastodon.example.org/@admin/99541947525187367",
+     "id": "http://mastodon.example.org/users/admin/statuses/99542391527669785/activity",
+     "cc": [
+       "http://mastodon.example.org/users/admin",
+       "http://mastodon.example.org/users/admin/followers"
+     ],
+     "atomUri": "http://mastodon.example.org/users/admin/statuses/99542391527669785/activity",
+     "actor": "http://mastodon.example.org/users/admin"
+   },
+   "id": "http://mastodon.example.org/users/admin#announces/100011594053806179/undo",
+   "actor": "http://mastodon.example.org/users/admin",
+   "@context": [
+     "http://www.w3.org/ns/activitystreams",
+     "http://w3id.org/security/v1",
+     {
+       "toot": "http://joinmastodon.org/ns#",
+       "sensitive": "as:sensitive",
+       "ostatus": "http://ostatus.org#",
+       "movedTo": "as:movedTo",
+       "manuallyApprovesFollowers": "as:manuallyApprovesFollowers",
+       "inReplyToAtomUri": "ostatus:inReplyToAtomUri",
+       "focalPoint": {
+         "@id": "toot:focalPoint",
+         "@container": "@list"
+       },
+       "featured": "toot:featured",
+       "conversation": "ostatus:conversation",
+       "atomUri": "ostatus:atomUri",
+       "Hashtag": "as:Hashtag",
+       "Emoji": "toot:Emoji"
+     }
+   ]
+}
diff --git a/test/web/activity_pub/activity_pub_test.exs b/test/web/activity_pub/activity_pub_test.exs
index d336fad95..a39ba9adb 100644
--- a/test/web/activity_pub/activity_pub_test.exs
+++ b/test/web/activity_pub/activity_pub_test.exs
@@ -302,6 +302,38 @@ defmodule Pleroma.Web.ActivityPub.ActivityPubTest do
     end
   end
 
+  describe "unannouncing an object" do
+    test "unannouncing a previously announced object" do
+      note_activity = insert(:note_activity)
+      object = Object.get_by_ap_id(note_activity.data["object"]["id"])
+      user = insert(:user)
+
+      # Unannouncing an object that is not announced does nothing
+      # {:ok, object} = ActivityPub.unannounce(user, object)
+      # assert object.data["announcement_count"] == 0
+
+      {:ok, announce_activity, object} = ActivityPub.announce(user, object)
+      assert object.data["announcement_count"] == 1
+
+      {:ok, unannounce_activity, activity, object} = ActivityPub.unannounce(user, object)
+      assert object.data["announcement_count"] == 0
+
+      assert activity == announce_activity
+
+      assert unannounce_activity.data["to"] == [
+               User.ap_followers(user),
+               announce_activity.data["actor"]
+             ]
+
+      assert unannounce_activity.data["type"] == "Undo"
+      assert unannounce_activity.data["object"] == announce_activity.data
+      assert unannounce_activity.data["actor"] == user.ap_id
+      assert unannounce_activity.data["context"] == announce_activity.data["context"]
+
+      assert Repo.get(Activity, announce_activity.id) == nil
+    end
+  end
+
   describe "uploading files" do
     test "copies the file to the configured folder" do
       file = %Plug.Upload{
diff --git a/test/web/activity_pub/transmogrifier_test.exs b/test/web/activity_pub/transmogrifier_test.exs
index eb093262f..a3408da9d 100644
--- a/test/web/activity_pub/transmogrifier_test.exs
+++ b/test/web/activity_pub/transmogrifier_test.exs
@@ -232,6 +232,34 @@ defmodule Pleroma.Web.ActivityPub.TransmogrifierTest do
 
       refute Repo.get(Activity, activity.id)
     end
+
+    test "it works for incoming unannounces with an existing notice" do
+      user = insert(:user)
+      {:ok, activity} = CommonAPI.post(user, %{"status" => "hey"})
+
+      announce_data =
+        File.read!("test/fixtures/mastodon-announce.json")
+        |> Poison.decode!()
+        |> Map.put("object", activity.data["object"]["id"])
+
+      {:ok, %Activity{data: announce_data, local: false}} =
+        Transmogrifier.handle_incoming(announce_data)
+
+      data =
+        File.read!("test/fixtures/mastodon-undo-announce.json")
+        |> Poison.decode!()
+        |> Map.put("object", announce_data)
+        |> Map.put("actor", announce_data["actor"])
+
+      {:ok, %Activity{data: data, local: false}} = Transmogrifier.handle_incoming(data)
+
+      assert data["type"] == "Undo"
+      assert data["object"]["type"] == "Announce"
+      assert data["object"]["object"] == activity.data["object"]["id"]
+
+      assert data["object"]["id"] ==
+               "http://mastodon.example.org/users/admin/statuses/99542391527669785/activity"
+    end
   end
 
   describe "prepare outgoing" do
diff --git a/test/web/mastodon_api/mastodon_api_controller_test.exs b/test/web/mastodon_api/mastodon_api_controller_test.exs
index 883ebc61e..882c92682 100644
--- a/test/web/mastodon_api/mastodon_api_controller_test.exs
+++ b/test/web/mastodon_api/mastodon_api_controller_test.exs
@@ -298,6 +298,24 @@ defmodule Pleroma.Web.MastodonAPI.MastodonAPIControllerTest do
     end
   end
 
+  describe "unreblogging" do
+    test "unreblogs and returns the unreblogged status", %{conn: conn} do
+      activity = insert(:note_activity)
+      user = insert(:user)
+
+      {:ok, _, _} = CommonAPI.repeat(activity.id, user)
+
+      conn =
+        conn
+        |> assign(:user, user)
+        |> post("/api/v1/statuses/#{activity.id}/unreblog")
+
+      assert %{"id" => id, "reblogged" => false, "reblogs_count" => 0} = json_response(conn, 200)
+
+      assert to_string(activity.id) == id
+    end
+  end
+
   describe "favoriting" do
     test "favs a status and returns it", %{conn: conn} do
       activity = insert(:note_activity)