diff --git a/CHANGELOG.md b/CHANGELOG.md
index 81b51c9..2bf7c1a 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -10,6 +10,7 @@
 
 ### Fixes and improvements
 
+- Fix form submission crash for anonymous attendees
 - Improve SMTP config and handling (#197)
 - Fix presentation slides URL (#200)
 - Fix custom S3 endpoint (#199)
diff --git a/lib/claper/forms.ex b/lib/claper/forms.ex
index f05daf0..2ec8931 100644
--- a/lib/claper/forms.ex
+++ b/lib/claper/forms.ex
@@ -324,6 +324,9 @@ defmodule Claper.Forms do
           nil -> broadcast({:ok, r, event_uuid}, :form_submit_created)
           _form_submit -> broadcast({:ok, r, event_uuid}, :form_submit_updated)
         end
+
+      {:error, changeset} ->
+        {:error, changeset}
     end
   end
 
@@ -344,6 +347,7 @@ defmodule Claper.Forms do
     |> Repo.delete()
     |> case do
       {:ok, r} -> broadcast({:ok, r, event_uuid}, :form_submit_deleted)
+      {:error, changeset} -> {:error, changeset}
     end
   end
 
diff --git a/lib/claper/forms/form_submit.ex b/lib/claper/forms/form_submit.ex
index f0c490f..3570e8d 100644
--- a/lib/claper/forms/form_submit.ex
+++ b/lib/claper/forms/form_submit.ex
@@ -25,6 +25,18 @@ defmodule Claper.Forms.FormSubmit do
   def changeset(form_submit, attrs) do
     form_submit
     |> cast(attrs, [:attendee_identifier, :user_id, :form_id, :response])
-    |> validate_required([:form_id, :user_id, :response])
+    |> validate_required([:form_id, :response])
+    |> validate_user_or_attendee()
+  end
+
+  defp validate_user_or_attendee(changeset) do
+    user_id = get_field(changeset, :user_id)
+    attendee_identifier = get_field(changeset, :attendee_identifier)
+
+    if is_nil(user_id) and is_nil(attendee_identifier) do
+      add_error(changeset, :user_id, "either user_id or attendee_identifier must be present")
+    else
+      changeset
+    end
   end
 end
diff --git a/lib/claper_web/live/event_live/form_component.ex b/lib/claper_web/live/event_live/form_component.ex
index e70ac45..b601e45 100644
--- a/lib/claper_web/live/event_live/form_component.ex
+++ b/lib/claper_web/live/event_live/form_component.ex
@@ -148,6 +148,9 @@ defmodule ClaperWeb.EventLive.FormComponent do
         {:noreply,
          socket
          |> assign(:current_form_submit, form_submit)}
+
+      {:error, _changeset} ->
+        {:noreply, socket}
     end
   end
 
@@ -167,6 +170,9 @@ defmodule ClaperWeb.EventLive.FormComponent do
         {:noreply,
          socket
          |> assign(:current_form_submit, form_submit)}
+
+      {:error, _changeset} ->
+        {:noreply, socket}
     end
   end
 
diff --git a/test/claper/forms_test.exs b/test/claper/forms_test.exs
index 5a299b2..63f1ccb 100644
--- a/test/claper/forms_test.exs
+++ b/test/claper/forms_test.exs
@@ -126,5 +126,62 @@ defmodule Claper.FormsTest do
                  }
                )
     end
+
+    test "create_or_update_form_submit/2 with attendee_identifier creates a form_submit" do
+      presentation_file = presentation_file_fixture(%{}, [:event])
+      f = form_fixture(%{presentation_file_id: presentation_file.id})
+
+      assert {:ok, %Claper.Forms.FormSubmit{} = form_submit} =
+               Forms.create_or_update_form_submit(
+                 presentation_file.event.uuid,
+                 %{
+                   "attendee_identifier" => "test-attendee-123",
+                   "form_id" => f.id,
+                   "response" => %{"Name" => "Daniel"}
+                 }
+               )
+
+      assert form_submit.attendee_identifier == "test-attendee-123"
+      assert is_nil(form_submit.user_id)
+      assert form_submit.form_id == f.id
+    end
+
+    test "create_or_update_form_submit/2 with attendee_identifier updates existing form_submit" do
+      presentation_file = presentation_file_fixture(%{}, [:event])
+      f = form_fixture(%{presentation_file_id: presentation_file.id})
+
+      {:ok, _first_submit} =
+        Forms.create_or_update_form_submit(
+          presentation_file.event.uuid,
+          %{
+            "attendee_identifier" => "test-attendee-123",
+            "form_id" => f.id,
+            "response" => %{"Name" => "Daniel"}
+          }
+        )
+
+      assert {:ok, %Claper.Forms.FormSubmit{} = updated_submit} =
+               Forms.create_or_update_form_submit(
+                 presentation_file.event.uuid,
+                 %{
+                   "attendee_identifier" => "test-attendee-123",
+                   "form_id" => f.id,
+                   "response" => %{"Name" => "Updated Name"}
+                 }
+               )
+
+      assert updated_submit.response == %{"Name" => "Updated Name"}
+    end
+
+    test "create_or_update_form_submit/2 without user_id or attendee_identifier returns error" do
+      presentation_file = presentation_file_fixture(%{}, [:event])
+      f = form_fixture(%{presentation_file_id: presentation_file.id})
+
+      assert {:error, %Ecto.Changeset{}} =
+               Forms.create_form_submit(%{
+                 form_id: f.id,
+                 response: %{"Name" => "Daniel"}
+               })
+    end
   end
 end