diff --git a/lib/pleroma/upload.ex b/lib/pleroma/upload.ex
index 1be1a3a5b..797555bff 100644
--- a/lib/pleroma/upload.ex
+++ b/lib/pleroma/upload.ex
@@ -67,6 +67,7 @@ def store(upload, opts \\ []) do
       {:ok,
        %{
          "type" => opts.activity_type,
+         "mediaType" => upload.content_type,
          "url" => [
            %{
              "type" => "Link",
diff --git a/test/web/activity_pub/object_validator_test.exs b/test/web/activity_pub/object_validator_test.exs
index ed6b84e8e..f9990bd2c 100644
--- a/test/web/activity_pub/object_validator_test.exs
+++ b/test/web/activity_pub/object_validator_test.exs
@@ -25,6 +25,8 @@ test "works with honkerific attachments" do
       assert {:ok, attachment} =
                AttachmentValidator.cast_and_validate(attachment)
                |> Ecto.Changeset.apply_action(:insert)
+
+      assert attachment.mediaType == "application/octet-stream"
     end
 
     test "it turns mastodon attachments into our attachments" do
@@ -48,6 +50,27 @@ test "it turns mastodon attachments into our attachments" do
                  mediaType: "image/jpeg"
                }
              ] = attachment.url
+
+      assert attachment.mediaType == "image/jpeg"
+    end
+
+    test "it handles our own uploads" do
+      user = insert(:user)
+
+      file = %Plug.Upload{
+        content_type: "image/jpg",
+        path: Path.absname("test/fixtures/image.jpg"),
+        filename: "an_image.jpg"
+      }
+
+      {:ok, attachment} = ActivityPub.upload(file, actor: user.ap_id)
+
+      {:ok, attachment} =
+        attachment.data
+        |> AttachmentValidator.cast_and_validate()
+        |> Ecto.Changeset.apply_action(:insert)
+
+      assert attachment.mediaType == "image/jpeg"
     end
   end