diff --git a/lib/pleroma/web/activity_pub/transmogrifier.ex b/lib/pleroma/web/activity_pub/transmogrifier.ex
index 5e07d5ea9..1367bc7e3 100644
--- a/lib/pleroma/web/activity_pub/transmogrifier.ex
+++ b/lib/pleroma/web/activity_pub/transmogrifier.ex
@@ -177,6 +177,12 @@ def fix_content_map(%{"contentMap" => content_map} = object) do
 
   def fix_content_map(object), do: object
 
+  # disallow objects with bogus IDs
+  def handle_incoming(%{"id" => nil}), do: :error
+  def handle_incoming(%{"id" => ""}), do: :error
+  # length of https:// = 8, should validate better, but good enough for now.
+  def handle_incoming(%{"id" => id}) when not (is_binary(id) and length(id) > 8), do: :error
+
   # TODO: validate those with a Ecto scheme
   # - tags
   # - emoji
diff --git a/test/web/activity_pub/transmogrifier_test.exs b/test/web/activity_pub/transmogrifier_test.exs
index e455da39f..e2926d495 100644
--- a/test/web/activity_pub/transmogrifier_test.exs
+++ b/test/web/activity_pub/transmogrifier_test.exs
@@ -615,6 +615,18 @@ test "it works for incoming rejects which are referenced by IRI only" do
 
       assert User.following?(follower, followed) == false
     end
+
+    test "it rejects activities without a valid ID" do
+      user = insert(:user)
+
+      data =
+        File.read!("test/fixtures/mastodon-follow-activity.json")
+        |> Poison.decode!()
+        |> Map.put("object", user.ap_id)
+        |> Map.put("id", "")
+
+      :error = Transmogrifier.handle_incoming(data)
+    end
   end
 
   describe "prepare outgoing" do