diff --git a/lib/pleroma/conversation/participation.ex b/lib/pleroma/conversation/participation.ex
index 121efb671..f1e1a6958 100644
--- a/lib/pleroma/conversation/participation.ex
+++ b/lib/pleroma/conversation/participation.ex
@@ -93,4 +93,10 @@ defmodule Pleroma.Conversation.Participation do
     end)
     |> Enum.filter(& &1.last_activity_id)
   end
+
+  def get(nil), do: nil
+
+  def get(id) do
+    Repo.get(__MODULE__, id)
+  end
 end
diff --git a/lib/pleroma/web/common_api/common_api.ex b/lib/pleroma/web/common_api/common_api.ex
index 2db58324b..86e95cd0f 100644
--- a/lib/pleroma/web/common_api/common_api.ex
+++ b/lib/pleroma/web/common_api/common_api.ex
@@ -4,6 +4,7 @@
 
 defmodule Pleroma.Web.CommonAPI do
   alias Pleroma.Activity
+  alias Pleroma.Conversation.Participation
   alias Pleroma.Formatter
   alias Pleroma.Object
   alias Pleroma.ThreadMute
@@ -171,21 +172,25 @@ defmodule Pleroma.Web.CommonAPI do
     end)
   end
 
-  def get_visibility(%{"visibility" => visibility}, in_reply_to)
+  def get_visibility(_, _, %Participation{}) do
+    {"direct", "direct"}
+  end
+
+  def get_visibility(%{"visibility" => visibility}, in_reply_to, _)
       when visibility in ~w{public unlisted private direct},
       do: {visibility, get_replied_to_visibility(in_reply_to)}
 
-  def get_visibility(%{"visibility" => "list:" <> list_id}, in_reply_to) do
+  def get_visibility(%{"visibility" => "list:" <> list_id}, in_reply_to, _) do
     visibility = {:list, String.to_integer(list_id)}
     {visibility, get_replied_to_visibility(in_reply_to)}
   end
 
-  def get_visibility(_, in_reply_to) when not is_nil(in_reply_to) do
+  def get_visibility(_, in_reply_to, _) when not is_nil(in_reply_to) do
     visibility = get_replied_to_visibility(in_reply_to)
     {visibility, visibility}
   end
 
-  def get_visibility(_, in_reply_to), do: {"public", get_replied_to_visibility(in_reply_to)}
+  def get_visibility(_, in_reply_to, _), do: {"public", get_replied_to_visibility(in_reply_to)}
 
   def get_replied_to_visibility(nil), do: nil
 
@@ -201,7 +206,9 @@ defmodule Pleroma.Web.CommonAPI do
     with status <- String.trim(status),
          attachments <- attachments_from_ids(data),
          in_reply_to <- get_replied_to_activity(data["in_reply_to_status_id"]),
-         {visibility, in_reply_to_visibility} <- get_visibility(data, in_reply_to),
+         in_reply_to_conversation <- Participation.get(data["in_reply_to_conversation_id"]),
+         {visibility, in_reply_to_visibility} <-
+           get_visibility(data, in_reply_to, in_reply_to_conversation),
          {_, false} <-
            {:private_to_public, in_reply_to_visibility == "direct" && visibility != "direct"},
          {content_html, mentions, tags} <-
@@ -214,7 +221,8 @@ defmodule Pleroma.Web.CommonAPI do
          mentioned_users <- for({_, mentioned_user} <- mentions, do: mentioned_user.ap_id),
          addressed_users <- get_addressed_users(mentioned_users, data["to"]),
          {poll, poll_emoji} <- make_poll_data(data),
-         {to, cc} <- get_to_and_cc(user, addressed_users, in_reply_to, visibility),
+         {to, cc} <-
+           get_to_and_cc(user, addressed_users, in_reply_to, visibility, in_reply_to_conversation),
          context <- make_context(in_reply_to),
          cw <- data["spoiler_text"] || "",
          sensitive <- data["sensitive"] || Enum.member?(tags, {"#nsfw", "nsfw"}),
diff --git a/lib/pleroma/web/common_api/utils.ex b/lib/pleroma/web/common_api/utils.ex
index d80fffa26..e70ba7d43 100644
--- a/lib/pleroma/web/common_api/utils.ex
+++ b/lib/pleroma/web/common_api/utils.ex
@@ -8,6 +8,7 @@ defmodule Pleroma.Web.CommonAPI.Utils do
   alias Calendar.Strftime
   alias Pleroma.Activity
   alias Pleroma.Config
+  alias Pleroma.Conversation.Participation
   alias Pleroma.Formatter
   alias Pleroma.Object
   alias Pleroma.Plugs.AuthenticationPlug
@@ -64,9 +65,21 @@ defmodule Pleroma.Web.CommonAPI.Utils do
     end)
   end
 
-  @spec get_to_and_cc(User.t(), list(String.t()), Activity.t() | nil, String.t()) ::
+  @spec get_to_and_cc(
+          User.t(),
+          list(String.t()),
+          Activity.t() | nil,
+          String.t(),
+          Participation.t() | nil
+        ) ::
           {list(String.t()), list(String.t())}
-  def get_to_and_cc(user, mentioned_users, inReplyTo, "public") do
+
+  def get_to_and_cc(_, _, _, _, %Participation{} = participation) do
+    participation = Repo.preload(participation, :recipients)
+    {Enum.map(participation.recipients, & &1.ap_id), []}
+  end
+
+  def get_to_and_cc(user, mentioned_users, inReplyTo, "public", _) do
     to = [Pleroma.Constants.as_public() | mentioned_users]
     cc = [user.follower_address]
 
@@ -77,7 +90,7 @@ defmodule Pleroma.Web.CommonAPI.Utils do
     end
   end
 
-  def get_to_and_cc(user, mentioned_users, inReplyTo, "unlisted") do
+  def get_to_and_cc(user, mentioned_users, inReplyTo, "unlisted", _) do
     to = [user.follower_address | mentioned_users]
     cc = [Pleroma.Constants.as_public()]
 
@@ -88,12 +101,12 @@ defmodule Pleroma.Web.CommonAPI.Utils do
     end
   end
 
-  def get_to_and_cc(user, mentioned_users, inReplyTo, "private") do
-    {to, cc} = get_to_and_cc(user, mentioned_users, inReplyTo, "direct")
+  def get_to_and_cc(user, mentioned_users, inReplyTo, "private", _) do
+    {to, cc} = get_to_and_cc(user, mentioned_users, inReplyTo, "direct", nil)
     {[user.follower_address | to], cc}
   end
 
-  def get_to_and_cc(_user, mentioned_users, inReplyTo, "direct") do
+  def get_to_and_cc(_user, mentioned_users, inReplyTo, "direct", _) do
     if inReplyTo do
       {Enum.uniq([inReplyTo.data["actor"] | mentioned_users]), []}
     else
@@ -101,7 +114,7 @@ defmodule Pleroma.Web.CommonAPI.Utils do
     end
   end
 
-  def get_to_and_cc(_user, mentions, _inReplyTo, {:list, _}), do: {mentions, []}
+  def get_to_and_cc(_user, mentions, _inReplyTo, {:list, _}, _), do: {mentions, []}
 
   def get_addressed_users(_, to) when is_list(to) do
     User.get_ap_ids_by_nicknames(to)
diff --git a/test/web/common_api/common_api_test.exs b/test/web/common_api/common_api_test.exs
index 16b3f121d..e2a5bf117 100644
--- a/test/web/common_api/common_api_test.exs
+++ b/test/web/common_api/common_api_test.exs
@@ -5,6 +5,7 @@
 defmodule Pleroma.Web.CommonAPITest do
   use Pleroma.DataCase
   alias Pleroma.Activity
+  alias Pleroma.Conversation.Participation
   alias Pleroma.Object
   alias Pleroma.User
   alias Pleroma.Web.ActivityPub.ActivityPub
@@ -12,6 +13,35 @@ defmodule Pleroma.Web.CommonAPITest do
 
   import Pleroma.Factory
 
+  test "when replying to a conversation / participation, it only mentions the recipients explicitly declared in the participation" do
+    har = insert(:user)
+    jafnhar = insert(:user)
+    tridi = insert(:user)
+
+    {:ok, activity} =
+      CommonAPI.post(har, %{
+        "status" => "@#{jafnhar.nickname} hey",
+        "visibility" => "direct"
+      })
+
+    assert har.ap_id in activity.recipients
+    assert jafnhar.ap_id in activity.recipients
+
+    [participation] = Participation.for_user(har)
+
+    {:ok, activity} =
+      CommonAPI.post(har, %{
+        "status" => "I don't really like @#{tridi.nickname}",
+        "visibility" => "direct",
+        "in_reply_to_status_id" => activity.id,
+        "in_reply_to_conversation_id" => participation.id
+      })
+
+    assert har.ap_id in activity.recipients
+    assert jafnhar.ap_id in activity.recipients
+    refute tridi.ap_id in activity.recipients
+  end
+
   test "with the safe_dm_mention option set, it does not mention people beyond the initial tags" do
     har = insert(:user)
     jafnhar = insert(:user)